For rear brakes that have to be screwed and you don't have the tool; Get a long pair on needle nose pliers and insert them into the notches, then take a crescent wrench and turn the needle nose pliers. If the piston is stuck and won't screw in with that trick at first, hit it with some penetrating oil, use a hammer and a flathead screwdriver or chisel and give it some diagonal love taps to get it to move back and forth. Hope this helps!
The threaded part inside is in a bearing so rotates as the pads wear down. Always pump the pads out against the disc before operating the park brake to ensure correct adjustment, after fitting the pads.