That's not easy and depends what is broken. Usually if the button goes up and down, the lock will work. There is a link between the perpendicular rod and the lock itself which might have come undone. You will have to remove the door panel to inspect it.
If it is the lock, the entire lock will need to be replaced, which is not cheap unless you have access to a pick&pull.

Klaus
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Volvoless. Sold the R. There is now a void...