How can I know if a text from Apple is real?

You don't have any viruses on your phone, it is a scam message designed to get you to purchase unnecessary software or phish for personal information.

Read more about it here -

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

Apple will never send a message like this.

Whoever is sending you the messages is trying to trick you into buying useless software that will do nothing to help your phone.....or worse....trick you into providing your personal information.

Ignore and delete any messages like this.