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

Hi, This only has one brake working properly. The other brake slides as It has lost a screw that keeps it in place on the handlebar. I started to disassemble the brake 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, it is very similar to a bicycle brake. Or it could be glue or taped in place, or another screw could be screwed in to the frame.