Those will be square taper cranks. They can be a pain to remove, but sometimes are okay. Remove circular plastic cap and there'll be a nut down inside the crank. One side will be left hand thread, the other right hand. You'll need a socket that is very thin walled. Undoing these can be hard, but getting the cranks off the square taper is usually the more annoying part as the cranks get jammed on. I've often had to bash them off with a hammer 😅

(If you're actually going to attempt this, probs worth watching a youtube tutorial)

Yeah, from what I understand, not easy to remove cranks without special tools. Dremel might work, but maybe a bike shop might be easier/safer/quicker.

Edit: short term fix, zip tie it to the tube so it doesn't move?