Use the pointed end of a spudger pry up the top edge of the motherboard, while keeping it clear of any cables or connectors.

Slide the motherboard toward the top edge, until it is free, and remove it.

Before reinstalling the motherboard, ensure the headphone jack gasket is properly seated. Then insert the motherboard gasket side first, insert the front-facing camera into it's recess, and lay the top edge of the motherboard into place.