My friends iPhone has gotten hacked

The message is a scam. All such messages are scams. Never, never, never download an app based on such a bogus message.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Miaaaaa15 Said:

"My friends phone has gotten hacked and it’s giving her 2 minutes to download this app with a credit card and she can’t download it or any of that and it notified her saying she has 11 viruses."

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That's a scam.

Apple would never send out such a text. That is a scam. And, having interacted with this message, most certainly have her consider performing the following:

Modify Apple Credentials:

• Modifying: her login credentials (using both a New eMail and a New Password) for Apple and each and all sites
• Associating: a different method of payment to her account
• Enabling: Two-Factor Authentication for Apple ID and for all other accounts that have such an applicable option

Your problem is completely different. You somehow installed a rogue calendar, probably accepting a “free” offer in an app or on a website.

iOS 13 or earlier: Go to Settings/Passwords & Accounts, scroll down to Subscribed Calendars, tap on the offender and delete it

iOS 14: Go to Settings/Calendar/Accounts and delete it under Subscribed Calendars

yea this has also happened to me and is coming up on my calendar and saying that i’ve got viruses and things like that can u help me please