Working at a brake shop we never ever adjusted disc brakes only drum brakes. I didn*t even know we had an adjustment.
I was quoted $250 for all four pads and rotors but then got a call to say the calipers were seized.
It ended up costing me $740 for one new rear caliper installed and they magically got the other one going.
About 6 months later, I was at a Mazda dealer where they ran my VIN to find out that both my rear calipers had already been replaced.
Our caliper might be different, but they have software called Mitchell that tells them everything about every car and being as he didn't look it up, it cost me $500.
As for the OP,.. If you've got your rear pads and rotors installed with the P-brake hooked up, you can just get in your car push the brake pedal hard, then pull the P-brake handle about 30-50 times.
This operates the self adjusters to set the rear calipers.
If you don't have your rear brakes installed or fully connected, you'll need to back off the calipers to make room for the thicker new pads.
You can also rotate your brake piston to turn it in but you could rip your boot if it's stuck to the piston and it's best to use the adjuster screws.
Hers a thread showing the internals of the rear calipers...
(Photobucket stole my pictures,.. I'll put them back in at the end of the thread.)
https://www.mazdas247.com/forum/showthread.php?123863018-Rear-caliper-dissection&highlight=