Pennywise

Glue and Trim/Brad (nail) gun would work.

Put a fin in a vise. Clamp the fuselage to the vise.

Don’t over clamp and press all the glue out.

I approve this message.

You wouldn’t know evil if it was staring you right in the face, multiplexer. :)

There is no fixing a broken cylinder like that unless you’re an expert and you know what you’re doing. Please don’t attempt to disassemble, puncture, drill, or cut the gas-cylinder itself.

The best way would be to get yourself a proper gas-cylinder removal tool, and watch some YouTube on how to use it and replace the gas-cylinder entirely.

I would suggest you just buy one replacement (you’re going to have to take it apart and see what you need) and then if everything works out then you can buy more.