My phone says unable to activate requires update

What do I do to get back in my phone?

Have you forgotten your passcode?, 

(< iOS 15.2) See this Apple article: If you forgot your iPhone passcode

If you forgot your iPhone passcode - Apple Support

(iOS 15.2 and newer) -> How to remove your iPhone, iPad, or iPod touch passcode without a computer

How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

iPhone 7

Optimize the range of the mobile network, see this Apple article:

If you see No Service, Searching, or SOS on your iPhone or iPad

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

If you still don't have a 'service' after that, see -> iPhone 7 Repair Program for "No Service" Issues

iPhone 7 Repair Program for "No Service" Issues - Apple Support

unable to activate requires update

See -> If you can't activate your iPhone or iPad (Wi-Fi + Cellular)

If you can't activate your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

• If you still can't activate your iPhone or iPad, contact Apple Support.