You need to find out what kind of ticket it is...
This is from the Reds website:
Rain Check Policies - In the event a regulation home game is not played, your rain check may be exchanged, subject to availability, at the main ticket office for a ticket to any subsequent regular-season home game during the current season. Any such exchange must be made through the main ticket office. Note that all paid Season Suite and Season Diamond, and Cincinnati Bell Technology Pavilion Seat Holders should follow the rain check instructions located on the back of their ticket. A rain check of a complimentary ticket (face value of $0.00) is not a valid rain check.