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For the general sequence, Tap or click > What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support — the seller will have to release the locks.

If this is Activation Lock and an Apple ID not yours, then the only one that can remove this lock is the person that holds the password to that Apple ID, or Apple given sufficient proof of ownership including the purchase receipt showing the serial number or IMEI and proof of identity. Activation Lock is intended as a theft deterrent mechanism, and nobody here can assist with bypassing. It.