Tvheadend

I have a tvheadend server, which is working very well.

However there are a few channels on my enigma 2 receiver which I cannot receive via the tuners on my tvheadend server.

I have exported these channels to an .m3u file via openewebif. The m3u file plays correctly via vlc.

I read that in 4.2 I can add this to tvheadend and make the channels available from there. However, I cannot find any documentation on how to do this. Adding it as a network and specifying it via local file fails.

Any instructions on how this can be done? Thanks for any help.