Computer issue

I put unbuntu linux on a lap top for my mom. I made it as super secure as I could. My mom being 80 has been hacked more times then i can count on her windows computer. She hates passwords and its like pulling teeth to get her to use strong passwords for anything.
So she has comcast come over to fix a phone issue. The guy got on this linux computer, t think he was fishing for her financial info. He wiped wiped the computer to cover his crime and loaded windows 11.
Is there any way to reverse engineer what he did and bring back linux and ann my security protocols.