Just installed I cannot change the speaker settings for rear speaker its there i just cant press it also no fader its on frony only.... anybody please

I was about to say "Check your wiring", but I don't believe the unit is wise enough to determine if speakers are connected or not.

Did it use to work and, suddenly, it stopped working?

Did you have to use an "Interface module" to tie in the head unit to the car? If so that could be the issue as the one I used to install my X950BH in my Chevy HHR said it did not allow the fade controls to work. Just a short sentence but easily missed I noted.

Try select the audio source to off and have the handbrake on.  You will be able to access the greyed out settings then.