Just open a bleeder should allow release of the pistons. Easy push back that way. To bleed after together attach a length of plastic tubing to the bleeder dropped into a can or similar of your dot 4 brake fluid. Keep the reservoir full to the recommended level during bleeding.

Since you mentioned it’s s 2015 with ABS, do not cycle your ignition on. You could have gotten some air in the caliper through the spot the brake fluid was coming out of. If it hasn’t happened yet, it will when you start working more on the caliper, especially with a rebuild.

When you turn your ignition on, the ABS self cycles as a diagnostic, to make sure it’s working. You don’t want to this to happen with air in the line. Bleed before turning the bike back on.

I’ve worked on motorcycle brakes more times than I can remember. For the future now I suppose, this thing has been way over complicated. 1) Always, I repeat always, loosen the master cylinder cap before compressing the brake pistons inward to relieve the back pressure. Failure to do so can over pressure the system, blow a seal, and cause leaks. Hopefully not, but if fluid is coming from where it’s not supposed to my guess is you’ve experienced this. The system isn’t designed to compensate for reverse pressure. 2) Do not pry with a screw driver or other implement because you run the risk of slipping and gouging something, and you don’t have a good feel for how much pressure you’re applying. Forcefully prying something on a brake system until it gives is always a bad idea especially if the master cylinder cap is still on. If the pistons don’t move freely something is wrong. Go to your local auto parts store and for about $10 buy a set of reverse snap ring pliers. You can buy a special tool for more money, but these work fine. They fit between the brake pads and push them apart without having to pry anything. Plus you can tell if you’re having to use undue force and stop before it gets really expensive.