What should I do if the handle and blade are not well combined?

The question is unclear, straight knife or folding knife? There are several handles with different knives. If the straight knife has a patch, you can sandwich a layer of red steel paper in the middle, or replace the whole handle of the screw or rivet, pour glue into the handle, heat it, insert the glue into the blade, wipe off the excess glue after drying, or polish the folding knife with sandpaper and replace the handle, patch, screw and glue.