Your tub faucet is held in place by a screw that attaches the handle to the base of the faucet. This set screw is the single part making the handle "loose" and you must replace it to fix the problem. The project only takes about a half-hour to complete. It requires no special tools or skills, just a handyman with a can-do attitude. If your faucet is wobbling or drooping, get ready to fix the issue once and for all.
Turn off the water to the tub as a precautionary measure. Shut the home's main water line by turning the valve by your water heater clockwise until it stops turning.
Search for the set screw on the base of the handle. On lever handles, it is usually seated around the bottom under the lever. On round, ball-shaped faucet handles, the screw might be underneath the plastic tab cap on top of the handle. Take this cap off by lifting it up with your fingers, and locate the screw under it. Turn the screw counterclockwise to remove it, using an Allen wrench.
Pull off the handle and inspect the bottom where the handle mounting hole is located. If it is broken or enlarged, replace the entire handle with a new one and tighten the set screw until the handle secures in place. If not, slide the handle back on and retighten the set screw with your Allen wrench.