No access to the tvheadend server today, but these are the things I did:
- first you have to have tvheadend compiled with zlib disabled, otherwise some files are not editables
- under the user running tvhend, locate the folder .hts/tvheadend in the home directory
- then something like input/dvb/networs/muxes
Yo need to identify the correct network and mux, not easy if you have many!
Then in the corresponding mux file, locate the jason part dealing with that service
and add a section containing the pid of the video it and the stream type H264
(you can use the jason file of a service working fine to understand what to type)
Does this helps?