How do I scan my iPhone for viruses

Assuming that you have not jailbroken your phone by installing unauthorized software, there are no known viruses for an iPhone or iPad.....so it is difficult to identify something that is not present on your phone.

Probably scam messages, but if you are really concerned, your best course of action would be to run Apple's Safety Check on your phone.

How Safety Check on iPhone works to keep you safe - Apple Support

Thee are no known viruses that can infect an iPhone. Scanning is unnecessary.

You saw scam messages that were trying to trick you into believing that there was a problem with your phone.

Never tap or click on a link in any messages like this. Simply delete them and move on.

Best point to remember......Apple will never send a message like the examples that you have seen, so you know they are scams that might look like they came from Apple, but they did not.