Use a brush or other applicator. Apply enough Flexa Fix to the damaged area. Be careful not to apply too much in one go as it can be difficult to manipulate. If necessary apply two or three coats to build up the joint area. Use epoxy blanket of pieces of polycarbonate to re-enforce if necessary.
You can also use the Flexa Fix to re-enforce the body corners (let the pure product leak into the corners) or to make flexible battery packs.