Do not repair what you have not confirmed is broken.

A lot of damage gets done fixing things that were working. You assume you know the fault, change something, and now there are two problems, one of which you created. Confirming that the thing you are about to repair is genuinely the thing at fault takes a fraction of the time it saves.

Before changing anything, find a way to check that your suspicion is right. Reproduce the fault, test the assumption, ask the person involved. If you cannot confirm it, that is worth knowing before you start rearranging things.