After giving away over a million free coffees on April Fool’s Day, Dunkin’ is at it again. The company confirmed to USA TODAY that the coffee chain is giving away another million coffees on Tuesday, April 21. Dunkin’ Rewards members can use promo code “FreeCoffee1” in their Dunkin’ app to redeem the offer starting at 9am local time on April 21, while supplies last. The company teased…