I will try to help.  I had to create a second internal tv_grab_file in the past and I think I remember.

In the TVHeadend userdata folder, you will find a directory named "epggrab".  Edit the file named "config".

It should look like this:
<pre>
{
	"channel_rename": false,
	"channel_renumber": true,
	"channel_reicon": false,
	"epgdb_periodicsave": 1,
	"cron": "4 */2 * * *",
	"ota_initial": true,
	"ota_cron": "# Default config (02:04 and 14:04 everyday)\n4 2 * * *\n4 14 * * *",
	"ota_timeout": 600,
	"modules": {
		"xmltv": {
			"class": "epggrab_mod_ext_xmltv",
			"dn_chnum": false,
			"name": "XMLTV",
			"type": "External",
			"enabled": false,
			"priority": 3
		},
		"pyepg": {
			"class": "epggrab_mod_ext_pyepg",
			"name": "PyEPG",
			"type": "External",
			"enabled": false,
			"priority": 4
		},
		"opentv-skyit": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky Italia",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-skyuk": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky UK",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-skynz": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky NZ",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-ausat": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Ausat",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"psip": {
			"class": "epggrab_mod_ota",
			"name": "PSIP: ATSC Grabber",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 1
		},
		"Bulsatcom_39E": {
			"class": "epggrab_mod_ota",
			"name": "Bulsatcom: Bula 39E",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"viasat_baltic": {
			"class": "epggrab_mod_ota",
			"name": "VIASAT: Baltic",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"nz_freeview": {
			"class": "epggrab_mod_ota",
			"name": "New Zealand: Freeview",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"uk_freeview": {
			"class": "epggrab_mod_ota",
			"name": "UK: Freeview",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"uk_freesat": {
			"class": "epggrab_mod_ota",
			"name": "UK: Freesat",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"eit": {
			"class": "epggrab_mod_ota",
			"name": "EIT: DVB Grabber",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 1
		}
	}
}

</pre>

Add an entry for your tv_find_grabbers and make sure the path is correct.  I'm showing my tv_grab_file entry below:
<pre>
		"/storage/.kodi/addons/service.tvheadend42/bin/tv_grab_file": {
			"class": "epggrab_mod_int_xmltv",
			"dn_chnum": 0,
			"name": "XMLTV: tv_grab_file is a simple grabber that can be configured through the addon settings from Kodi",
			"type": "Internal",
			"enabled": true,
			"priority": 6
		},

</pre>

The final "config" file should look like this: (notice I added my entry on the top of the list)
<pre>
{
	"channel_rename": false,
	"channel_renumber": true,
	"channel_reicon": false,
	"epgdb_periodicsave": 1,
	"cron": "4 */2 * * *",
	"ota_initial": true,
	"ota_cron": "# Default config (02:04 and 14:04 everyday)\n4 2 * * *\n4 14 * * *",
	"ota_timeout": 600,
	"modules": {
		"/storage/.kodi/addons/service.tvheadend42/bin/tv_grab_file": {
			"class": "epggrab_mod_int_xmltv",
			"dn_chnum": 0,
			"name": "XMLTV: tv_grab_file is a simple grabber that can be configured through the addon settings from Kodi",
			"type": "Internal",
			"enabled": true,
			"priority": 6
		},
		"xmltv": {
			"class": "epggrab_mod_ext_xmltv",
			"dn_chnum": false,
			"name": "XMLTV",
			"type": "External",
			"enabled": false,
			"priority": 3
		},
		"pyepg": {
			"class": "epggrab_mod_ext_pyepg",
			"name": "PyEPG",
			"type": "External",
			"enabled": false,
			"priority": 4
		},
		"opentv-skyit": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky Italia",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-skyuk": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky UK",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-skynz": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Sky NZ",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"opentv-ausat": {
			"class": "epggrab_mod_ota",
			"name": "OpenTV: Ausat",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 2
		},
		"psip": {
			"class": "epggrab_mod_ota",
			"name": "PSIP: ATSC Grabber",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 1
		},
		"Bulsatcom_39E": {
			"class": "epggrab_mod_ota",
			"name": "Bulsatcom: Bula 39E",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"viasat_baltic": {
			"class": "epggrab_mod_ota",
			"name": "VIASAT: Baltic",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"nz_freeview": {
			"class": "epggrab_mod_ota",
			"name": "New Zealand: Freeview",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"uk_freeview": {
			"class": "epggrab_mod_ota",
			"name": "UK: Freeview",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"uk_freesat": {
			"class": "epggrab_mod_ota",
			"name": "UK: Freesat",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 5
		},
		"eit": {
			"class": "epggrab_mod_ota",
			"name": "EIT: DVB Grabber",
			"type": "Over-the-air",
			"enabled": false,
			"priority": 1
		}
	}
}

</pre>