Transpose for tenor sax

Not clear how to transpose a chart for say, tenor sax, without changing the backing key. Eg if a song is in Bb then the tenor part is written in C, but surely it's not enough just to change the key of the song 'cause that would change the playalong key. Sorry if this sounds dumb!

Using song-transpose changes the key of just that chart (AND it's play-along)
You want global-transpose. That changes the displayed chords in ALL your charts. The player still plays in concert-key.

Check the tutorials in Settings > Help
:))BOB