I do not know previous owner of ipad

You don't.

This iPad is a dead, useless device to you.

We cannot help you and Apple will not help you either since you are not this iPad’s original owner.

Activation Lock is a anti-theft, personal data protection feature that cannot be defeated without the help of the iPad’s original owner.

Get you money back for this device, if you can.

Tap and read this extensive user tip on the pitfills of purchasing or getting a used iDevice.

The All Too Common SAD Reality of Buying … - Apple Community

Unfortunately, you cannot. Only the previous owner can. Can you get a refund?