The dipstick goes directly into the oil sump, if it's actually loose, then i presume some oil would be leaking out.
I presume your engine is 1ZR-FE, here's a picture where it's clearly visible how the dipstick tube i's attached to the engine.
The tube should be flexible enough to be able to pop it out a bit, and just to slip a new ring. If the tube is moving, then see if it's possible to tighten that one screw, which holds it down.