A loose door knob or lever usually comes from mounting screws, a set screw, or play in the spindle. Repair starts by identifying which part moves and tightening only the correct fastener, because overtightening small screws can strip threads or damage the mechanism.
Find which part is actually loose
Hold the trim plate against the door and move only the knob or lever. If it rotates on the spindle, look for its set screw; if the whole assembly moves, inspect the screws that clamp the two sides together.
Tighten mounting screws evenly
Alternate between mounting screws so the trim stays flat and the latch still moves freely. Stop when the assembly is firm; tightening until the door or mechanism distorts can create binding and break parts.
Seat the set screw on the correct part of the spindle
On models with a small side screw, align the handle and tighten it against the intended flat or groove on the spindle. If the screw will not hold because its threads are damaged, replacement is better than adding glue.
Replace worn parts if the looseness returns
A worn spring, spindle, or bushing can stay loose even when screws are tight. If the latch does not return, the lever droops, or play immediately returns, replace the worn component or the lockset.