Alek, Clamp your bow to a form with the belly up. Then use a heat gun to heat the wood, a section at a time, until it is chocolate brown(not black) then let it stay clamped for 3 or more days so the wood can rehydrate before stressing it.
In the new TBB4, Marc St Louis, who popularized this method, has a whole chapter on heat treating(tempering) bow bellies. Pat