What part got stuck? I literally just charged my system two hours ago, and it's just a cap, I didn't see anything that can get stuck.
Or are you talking about the fitting on the hose that the refrigerant can screws into?
Edit- Ok, I see, you mean like this-
Maybe flathead screwdriver that is slightly larger than the open part of the cap?
Or heat up needle nose pliers so they melt into the side so you can twist it out.
Or a reverse-thread puller for stripped screws might work.
Or heat up the top of the screwdriver.
Whatever you do, just be careful you don't push too hard in the center so you don't release the refrigerant!