Somewhat what James just said,
Grab the slide with your left hand, left thumb toward you and your fingers grasping the right side of the slide. Use a strong grip.
Now with your right hand. Using a strong forward movement jam it forward , (this will engage the grip safety) and move the slide rearward with sufficient force.
This works with 1911's with a stuck case as well.
As always, use proper safety rules. either the case is a bad reload with damaged case, cracked case, etc.
This works on the firing line when you have to clear a jam and can't take it to a safe area. I use this for IPSCand Idpa when i have a stuck case.
Inspect you ejector as well after the case is out and make sure it isn't cracked, etc.
Let us know how it worked.