mobility walker with trays, one brake faulty. (Southgate N14)

Hi, This only has one brake working. It has lost a screw in the brake by the handle that, if there, stops it sliding along the handle bar. I started to disassemble it to put a screw in, but haven't managed to take it apart enough, and got bored with it. I'm sure it can be fixed by someone more patient that me. Or it could be taped in place.