Hello. I bought phone from someone and activation is lock. Can you help me with it?

No. No one can help you other than the owner of the account that was used to lock the device.

There is no way to bypass the activation lock.

If the seller can't or won't remove the lock and you can't return it for a refund, turn it over to the police. It's probably stolen.

Activation Lock is a theft deterrent feature with no bypass or workaround.

Without the owner's authorisation, no thief or anyone including you can re-use the device.