The handles on internal doors are usually fairly simple mechanisms and any that fail can usually repaired quickly and inexpensively by a tradesman. If the mechanism has become stiff or stuck then some adjustment, lubrication or taking the unit apart before re-assembly may sort out the problem.
If one of the interior working parts has broken or come away from the mechanism then your tradesman should be able to mend, reattach or replace the part in question. Similarly they may also be able to repair or replace the handles themselves. Older ceramic, porcelain, bakelite or plastic handles can crack with age, but they can usually be repaired with adhesive by a skilled hand.
Where a handle, or the fittings for a handle, are coming away from an internal door then your carpenter or joiner should be able to remove the handle and fill the screw holes or make them more secure. They can then reattach the door handles once any patching is complete and any glues or fillers used to make a repair have dried.
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