I have two side-by-side exterior screen doors on the front of my house. One side has a functioning handle that turns, locks, and has a latch.

The other door has a top slide that keeps it closed. The handle is supposed to stay still. However, the dummy handle is a lever, and instead of staying still, it is loose and flops down. The handles on both sides of that door are securely affixed to the spindle that goes through the door. But if I lift the lever to make it properly horizontal, it just flops back to the perpendicular position.

How can I tighten the handle?