Do you know which transmitters serve your area.
If not look at this,
https://www.freeview.co.uk/corporate/detailed-transmitter-information
If you are being served by two transmitters (that have good signal quality) make a note of their names and the multiplexes they broadcast on.
The multiplex (mux) number is under the black circle with the white N.
Do a search for each transmitters information which should determine which ITV regions are being broadcast to you.
If you only want to receive signals from one transmitter with the ITV region you prefer you can do a manual tune
using the mux numbers you made a note of.
To clear the channels stored on your TV try unplugging the aerial cable and doing an Auto Channel Search
and see if that clears them. If it does then you can proceed with the manual search.
If the above does not clear the auto tuned channels you may have to do a Factory Reset.
