how to unlock activation lock on new imac

I have the same problem, after giving password to install new update an new imac, after installation hat asked for password. I think I gave the right after several trying got looked. Changed on iPad New password but too late, IMac is looked. Any recommendations? Thanks

How to remove Activation Lock – Apple Support (UK)

If your iMac is Activation Locked than it is definitely NOT new and is quite likely stolen. Return it for a refund immediately.

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