I bought was given a iPhone XR but it has a activation lock on it and the previous owner doesn’t know the password what do I do

Ask the person whose Apple ID that is to use Apple's iForgot service or contact their Account Security team, or the iPhone’s original owner to supply Apple with its purchase receipt and ask them to remove the lock.

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Have the previous owner enter the Apple (iCloud) ID and click Forgot Password.

Apple ID - Manage

Apple ID – Forgot Password