Fix a task swivel chair with a loose back
Most task chairs have 2 or 3 levers to adjust the angle of the back and seat (for 3 levers).
If either one won't hold in place then there is often an easy fix.
Turn the chair over and on the opposite side of the lever there will be a nut. If you can't see one then it is probably cover by a plastic cap. If so take the cap off.
Then give the nut a little tighten until the lever starts holding the back or seat angle again.