Trying to fit new rear pads on 1995 gti (ABS) got them all apart lovely jubbly, but could I compress the piston!

It said on the instructions with the brake pads (no manual)(Pagid pads) that for rear pads the piston should be turned or take up adjustment on screw

I could do nither, couldn't see any adjusting screw could not turn piston? Please can anybody enlighten me or direct me to a site with detailed instructions?
Many thanks in anticipation

Russell