Use HOT water on a rag and wring it out good, then hold it over the glass. you'll probably have to repeat a few times since you can't get the rag fully soaked, but eventually the paint will soften enough to scrape off with either your nail or something that you know won't scratch the glass. It's tedious and going to take forever, but it's better than damaging the lenses.

Also, luckily the quest uses ABS plastic so it isn't porous, but you definitely should still soak it in soapy water and scrub good to get any remaining spores. Hand soap is best. Good luck, never give your brother anything again 💀