You replace them!
To fix a stuck front brake caliper on a 1990 Toyota SR5 pickup, start by safely lifting the vehicle and removing the wheel. Inspect the caliper for any signs of damage or corrosion, and clean it thoroughly to remove dirt and debris. If the caliper piston is stuck, use a brake caliper tool to compress and retract it, or replace the caliper if necessary. Finally, ensure the brake hoses are not pinched and bleed the brake system to remove any air before reassembling and testing the brakes.
Your bike disc brakes may be stuck closed due to dirt or debris, a misaligned caliper, or a problem with the brake pads. To fix this issue, you can try cleaning the brake system, adjusting the caliper alignment, or replacing the brake pads if they are worn out. If the problem persists, it may be best to seek help from a professional bike mechanic.
You need to replace your brake caliper on the side that drags. The caliper has several parts (piston & slider) that corrode and get "stuck". The only way to fix the problem is to replace the caliper. If you try cleaning the parts, it will most likely stick again within a few months.
if the caliper is stuck u need to replace the caliper it is also a wise move to buy a matched pair of calipers, cheaper , and replace both sides at same time
just replace the whole caliper.
Replace
Sticky/stuck caliper slides, sticky/stuck caliper piston, collapsed brake hose, pinched brake line,
A stuck caliper piston. Stuck caliper slide pins. Pinched brake line/hose. Frozen/stuck parking brake cable/mechanism.
If the caliper is sticking or leaking it is possible to buy a rebuild kit and replace all parts that are worn inside. If the caliper has a cracked or broken housing then the unit can not be repaired and must be replaced.
To remove the caliper and rotor from a 1995 Buick Regal, first ensure the vehicle is securely lifted and supported. Next, remove the wheel and then the caliper by loosening the caliper bolts; if it's stuck, try tapping it gently with a hammer or using a brake caliper tool to compress the piston slightly. Once the caliper is free, hang it safely without stressing the brake line. If the rotor is stuck, you may need to tap it with a rubber mallet or use penetrating oil to help loosen it.
You can find detailed instructions on fixing Stuck brake sliders on youtube.com/watch?v=KpNlOnZiiFE
They can be rebuilt but not by a novice. Replace it with a rebuilt unit.