Go film and interview every place and person where covid-19 evidence should exist, and ask those people for hard evidence. But you yourself has to act like a Covid believer.

But explain them that there are few deranged conspiracy theorist and anti-vaxxers who don't want to wear mask and are putting your and your grandma's lives in danger. So you need evidence that Covid-19 exist to convince them to comply with the rules.

Go to hospitals, doctors, mortuary, graveyards. At least find those people who manage those places and ask for physical evidence. Ask them for evidence from people who died because they didn't wear a mask.

When you're done you can also ask the person to sell his car. If he doesn't want to sell it. Ask him "if they are that selfish that they wants someone to die in a traffic accident?" And show them the numbers of people dying in traffic accidents.