All I can give you is this: Bug in Scanning DVB-T2 with QAM256 in UK - #2 by OttoKerner
You need to find the right .ini file which was used before. Then make the changes Re: frequency and symbol rate etc for the new channel setup.
Then delete the tuner in plex and set up a completely new one.
Keep in mind that Plex will not access encrypted channels or those which have been marked as “recording prohibited”. (which can possibly mean all channels within a station bouquet)
The ini files are located on Windows in here:
C:\Program Files\Plex\Plex Media Server\Resources\Tuner\Shared\scanners\
and on Linux they can be here /usr/lib/plexmediaserver/Resources/Tuner/Shared/scanners/ (or whatever equivalent location your particular platform uses).
