How to fix the speaker

Assuming it's not a software problem that can be resolved by things like a software update or factory reset, the only thing I can come up with would be to replace the speaker and hope that fixes the problem. There may be other users who have different things to try first though; hopefully someone will chime in and offer some suggestions.

If you do get to the point where you decide that you need to replace the speaker, I did find a guide that will show you how to do that.

Samsung Galaxy A52 screen replacement - repair guide

As the title suggests, this is a guide to replacing the screen which I know isn't what you want, but one of the steps along the way is to remove the speaker. So all you have to do is follow the guide up to Step 10 and stop there, then when you have the new speaker in place, follow the instructions in reverse to put it all back together again. As near as I can tell, for replacement parts you'll need a new speaker and precut adhesive for the rear case.

Hope this helps; let us know how it goes!