ignore it
You were surfing and you got this popup from a webpage?
It's a scam. At best it wants you to pay to download something that doesn't work (there's a reason that program it's telling you to download isn't in the app store, it's not a good program)
iPads cannot get viruses. A virus is a malicious program that propogates itself across the operating system and file manger part of the device. The iPad doesn't have a file manager to corrupt so it can't get a virus.
Don't try to download anything, don't pay for anything, and i'd consider not visiting that website again.
You may need to go into the settings, safari and remove your history from your ipad, just to fully remove that popup but you can't get the virus it's trying to tell you that you can.