That could be the problem, this is an old version. The screenshot that I showed was from v4.3.
Try going into Configuration -> General -> Base and make sure that your 'Default view level' is 'Expert' and saved.
If you scroll down further to the 'Miscellaneous Settings' section, do you see an option for 'DVB scan files path'? (This may be a v4.3 feature. I'm not sure when it was added.)
If you do, you could go into /usr/share/kodi/addons/service.tvheadendicetv/dvb-scan
and find the predefined muxes for your location. Copy that file to somewhere else in /storage
and modify the file(s). Once this is done, change the DVB scan location above and try again.
Also, go to the LibreELEC forum, somebody there may have encountered this issue too.