Second hand iphone 11

You can't, I'm afraid- your best bet is to post signs around and/or give it to local authorities. As long as the device is powered on and connected to a network, it can be tracked with Find My, so the owner may be able to reclaim it.

If you are talking about "activation lock" (an anti-theft measure), AND if you cannot remember the old Apple ID & Password (even using these instructions:--> If you forgot your Apple ID email address or phone number - Apple Support or these:--> If you forgot your Apple ID password - Apple Support ) neither we, just users like you, nor Apple can help you, sorry, unless you are the original owner and you still have the proof of purchase (receipt/invoice reporting your device’s IMEI or Serial Number). Should be this case, start your request using this link: https://al-support.apple.com/#/additional-support

Shouldn’t be this case, activation lock can be removed only by the previous owner, with the credentials that were used to activate that iPhone/iPad. Without those credentials, that device is useless to you.

You can also take a look at this support article:--> How to removeActivation Lock- Apple Support

Regards

Giulio

I would return it back to the seller, if he can't remove it then don't waste your money on this device, only the one who enabled activation lock can disable it.

How to remove Activation Lock - Apple Support

I’m afraid you’ve been scammed. An Activation Locked device cannot be opened by anyone except the person it's locked to. If you aren't able to return it for a refund, the device is useless to you.

You can recycle it if you wish at any Apple Store.

The All Too Common SAD Reality of Buying … - Apple Community