Just lay a patch of UC over the area about 1/2" larger than the hole.

Cut the corners at a 45 degree angle (or round them off) just so you don't have any sharp corners (They can lift).

A regular iron will work, start with the lowest setting until it starts to stick.

Do the corners first, keeping it fairly staright and wrinkle free. Then work the iron from one end to the other back and forth.

Increase the heat and repeat until all of the wrinkles are out.

The bad news is, you'll lose some of your decal, but you could always try to touch that up later with a little paint (or blue covering)