my son got a security lock out message

To unlock your iPhone, follow the steps described in the Apple article:

(< iOS 15.2) -> If you forgot your iPhone passcode

If you forgot your iPhone passcode - Apple Support

• If you don't have a computer and you can't borrow one, you need to go to an Apple Retail Store or Apple Authorized Service Provider for help.

(iOS 15.2 and newer) you don’t need to have a computer -> If you see an iPhone or iPad unavailable message or Security Lockout screen

https://support.apple.com/en-us/HT212951

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Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID

If you forgot your Apple ID email address or phone number - Apple Support                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

See -> If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

As the Device is passcode locked, you need to erase the device but if the Find My on after erasing it will show the iPhone locked to the owner(Activation Lock) To unlock that you need an Apple ID and password. If he doesn’t know the password you can use - If you forgot your Apple ID password - Apple Support (CA)

But If you can not able to recto recover the account then you can submit Proof of purchase to Apple using - How to remove Activation Lock - Apple Support (CA)