Help with Beretta 391

[New Shotgunner]

I have a 391 that a "Friend" put away for me and he failed to install the Red spacer in the fore-end before he put the end cap on. The end cap is now stuck. The pin it rides on is in the fore-end is into the center of the cap and keeps it from twisting off as it should. I can't retract the pin in the small space between the fore-end and end cap and I can't get to the back of the hole where the pin resides to remove it because of other parts in the fore-end. Does anyone have a solution to this problem?

I can't be the first one to have this happen. I was hoping to shoot this weekend and of course Beretta is closed until Monday. I would appreciate any suggestions.