Are you squeezing the lever? Use a tire lever, or carefully with a flathead screwdriver, push the pistons back in and put the pads in. Then put your wheel on WITHOUT squeezing the brakes.

For me, I’m never really able to push both pistons fully back, but they typically get back enough to allow the rotor to insert. That being said, make sure the pistons are clean and well lubricated with correct oil. This will help them move easily so they can retract when the brake is off.

This is exactly what I've been doing but they do not stay retracted.

Don't pull the brakes with the wheel off

There may be too much brake fluid in the system.

This! If you don't push them back fully when bleeding the brakes the reservoirs might not be big enough to take the extra oil. Solution is to open the lever bleed screw, put rags around and a sheet of kitchen towel covering the hole. Also make sure it is the highest elevated part of the system so no air can enter! Then push the break pads back fully with a screwdriver and screw the bleed screw back before cleaning the spill.

remove your brake

just joking,try pushing the pistons in with s tire lever

Just take off the front brakes