How do I tighten chair legs that are loose at the seat end?

Use a mallet to tape the seat up and away from the legs. When the seat is just starting to slip off the leg you coat the leg with wood glue and then drive the seat bacl onto the leg. Allow the glue to cure with the chair upside down over night.

Hi, pineknotter1!

What is the chair made of, please? Wood, metal, plastic or maybe even combinations of different materials?

If it's made of wood, then gluing might be needed. But, it would be a good idea to look for any screws under the seat that you can tighten first. There could also be other types of fasteners used, so you might need to tighten them also.

Thanks!