I think that I have virus

on unjailbroken ios devices the only way to get new software is app store

virus is software too

you can't get software from mails, websites, sms's or the likes

popups which claim you have a virus are scam

odd behavior of your device is more likely to be a software bug or a hardware defect

what makes you think you have a virus ?

See this discussion: https://discussions.apple.com/thread/251048833