How do I get rid of activation lock on my iPhone

Okay so I had my apple watch series 2 paired with my iphone 6 and I got a new iphone 8 plus. The same week, my iphone 6 got locked (my nephew tried entering the code various times) and I unlocked it via itunes and then when I tried unpairing my watch from previous iphone (6), I couldn’t find it in the list of connected devices.

Now when I try to connect my apple watch to the new iphone (8 plus) it says that an activation lock is enabled. Please help me get rid of it.