Here’s step 1: https://support.formlabs.com/s/article/Cleaning-the-Glass-Optical-Window-Form2
For the mirror and galvos, reach out to Formlabs Support and they’ll send you the cleaning instructions. I think they avoid posting the docs publicly as they like to confirm cleaning is necessary before you proceed (cleaning too often or improperly can damage those sensitive parts, and it’s also possible sometimes there are other things going on).
Cleaning really does make a huge difference; take a look at my first picture here (and that’s one I caught pretty suddenly - when the contamination gets worse the effects can get dramatically worse than seen there).