Loosening the truss rod.

You'll need to loosen the A string to move it out of the way.

Important!
Turn the wrench counter-clockwise
only 1/4 turn.

You should be able to see a difference after a quarter turn. If not, try a little more, but I'd recommend no more than a half a turn per day. Wooden necks require time to "settle in" to truss rod adjustments.