How to get rid of Adobe Flash Player update pop-up?
Hold the Windows Key and press “R” to bring up the “Run” dialog box.
Type “services.msc“, then press “Enter“.
Double-click the “Adobe Flash Player Update Service“.
For the “Startup type“, choose “Disabled“.
Select “OK” and close the “Services” window.
I don't have the problem and don't have that service but I was able to get to the services.msc box and detail no problem.
I got it from a Google search.
https://www.google.com/search?client=firefox-b-1-d&q=adobe+popup+virus