If you haven't got the tool, you can use a very large screwdriver and brute
force to screw the pistons back!
Of course if those pistons are running nice and free it'll work! if they are
slightly seized your in for a job!
Did have a tool for them, got it from Snap-on £30 ($49) came with adapters
for other cars.
Sure any good tool shop would have one.......