How do i get activation lock off of my iphone

You are likely in possession of a stolen phone. Activation Lock is a theft prevention feature and the fact that the seller did not clear the lock indicates that it might have been stolen. It will remain useless for you, so you could turn it in to the police or recycle it at any Apple Store.

You will need the credentials for the account used to lock it.

There is no way to bypass the activation lock.