I have my iphone 7 was given to from my uncle who live in austrila

The owner forgot his email and he lose his mobile number

He can check his mail box and contact his carrier.

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See the following Apple articles:

Activation Lock for iPhone, iPad, and iPod touch

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

How to remove Activation Lock -> How to remove Activation Lock – Apple Support (UK)

• If you need help removing Activation Lock and have proof of purchase documentation, you can start an Activation Lock support request.

Read this before you use a 2nd hand iPhone.

You can also contact Apple support for help, -> Get Support (apple.com)

You have to show proof of ownership of your product, provide all documentation showing your purchase of the device.

If you do not have additional proof of ownership, contact the reseller. They may be able to provide the original purchase document.

Once Apple receive your proof of ownership, Apple will further review your request and provide an update.

See also -> Keep your receipt after you buy an Apple device

Keep your receipt after you buy an Apple device – Apple Support (UK)

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Perhaps you have got a stolen iPhone.

Your uncle need to read -> this Apple article: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch -> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Then has to remove the iPhone from his account, see this Apple article:

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

Then you can sign in with your own Apple ID.

Lets put it like this perhaps ive got a lost and found iphone xs. Given to me by a relative from australia. Ive got the apple ID, since it has a cue word and i also got the password derived from the apple id. Now it says it is LOCK For security reasons… apple suggest to enable password in the appleid.apple.com. However , it ask the mobile number which i do not have, what will i do to open this iphone XS?

thanks.