Stop the source of the water before attempting to dry the plywood. Bring rained-on plywood indoors, or stop the leak that dampened structural plywood in your home.
Wipe down the plywood with clean rags to soak up as much as the surface moisture as possible.
Point several high-powered fans at the plywood to dry it out. Stand the plywood to let the air flow hit as much plywood surface area as possible.
Place a space heater behind the fans to speed up the drying process, if desired. Situating freestanding plywood and fans close to a furnace works as well. However, the Engineered Wood Association warns that plywood that is dried too quickly can suffer from raised surface grains, which lessens the visual appeal of the panel.
Keep the fans blowing until the plywood dries. Expect a freestanding sheet of plywood close to a heat source to dry in a few days, while a piece of plywood composing the structure of a house can take up to a month to dry.