Bathroom renovation, replacement of the bathtub faucet

Hello everyone,

I just came across this forum and hope you can help me a bit.
We have bought a house and are currently renovating it. Of course, if possible, doing it ourselves.
One of the bathrooms was already renovated once 6 years ago and should remain that way.
What we have noticed, however, is that in the bathtub the switching from shower to water outlet on the concealed faucet no longer works correctly. The pin for the switching is under the lever and is difficult to remove or switch, and when showering, water always flows from the tap as well.
Is it possible to simply replace something like that with another faucet or only with the previously installed one?
Unfortunately, I have hardly any experience regarding what to pay attention to. It’s not just about replacing a normal tap, that would be no problem.

Either the switch can be made operable/repairable again or replaced with original parts.
[Abbildung] could help further.

So no idea if the diverter can be made functional again, but the valve itself is already strange. We would prefer to completely replace it with another one. Attached is a picture

The plumber should handle the replacement anyway, so he can also inspect the [Armatur] for a repair.

well, I can manage to replace the fitting myself. only finding a suitable replacement is probably not that easy. especially because it shouldn’t be the same model again.

Get the exact model and then see what the manufacturer offers. The big/expensive ones either have one universal valve body for everything (Hansgrohe) or the same valve body for a number of models. After 6 years you might still be lucky and other fittings fit the valve body. With hardware store goods you usually have bad luck.