How do I remove virus notifications from iPhone apps?

The top right of each app displays the number of notifications from that app. That is not the number of viruses you have. Your iPhone isn’t even susceptible to viruses. To remove the notifications, open that app and see where they are coming from.

Not sure what you mean without a screenshot of what issue you’re having. But viruses are not common on iOS.

1.) if it’s in your browser you need to delete cache and cookies or just reset the whole browser. Visiting explicit sites often loads the “!!! Your iPhone has a virus!! Click to delete!!!” Bs into your phone. I think it’s stored in cache so just reset the browser.

2.) if you jailbroke your phone or you downloaded an app from an untrusted source you can always back up your phone and perform a factory reset

3.) if for some reason you mean all of your apps now have a tab by them with a number inside you’ve likely enabled voice control which you can disable by going to Settings > Accessibility > Voice Control.