how can I unlock activation lock on iphone se

If this is a used device, you will need to contact the previous owner to have them log out of iCloud or go to iCloud.com/Find My Phone and erase the device, then remove it from their account. If you can’t do that, the device is useless. 

Activation Lock - Turn off Find My iPhone 

If necessary, if you are the original owner, take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store.

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or contact Apple ID Support. They will need to see the original purchase receipt/paperwork also.

Apple ID Support

Apple ID Support (2) 

Apple Support by e-mail or chat         

Apple Support using Twitter

Or fill out and submit this form.