The A roll will rewind automatically at the end of the last tune on
the roll.  There is no method of rewinding the roll earlier than that
unless you modify the pneumatics to incorporate an exhaust to atmosphere
operated by some form of small manually operated valve, teed into the
rewind port.  This sort of modification is not to be encouraged.

I can see no reason why anyone would wish to rewind an A roll before
the end!

Best wishes, Nicholas Simons