I use the song app,question if I tune in open g with the 6th string how to I follow in your song app when I play a Stones song.
Chords and chords and the same chords go together no matter how your guitar is tuned.
The secret to playing along if you are in open G is no secret. You simply have to know the names of the chords that your fingers are making. Some of them may have extended names beyond the usual in which case be guided by their letter name derived from the chords root and the sound when you play.
Welcome back, @fasteddymac !