A fair amount of people flip the cupped boards successfully and they'll relax back down. Before you do anything though, be sure there's a sufficient amount of ventilation under the deck itself. Poor ventilation will lead to cupping and/or unwanted movement. 24" off the ground is ideal for the most part.

When I install deck boards I try to remember the saying "cup is up" i.e. the growth rings should be cupped upward when looking at the edge. That way when they dry out the edges bend downward.