1. From Sales, click Group Sales
  2. Select the reservation from the calendar
  3. In the pricing grid, click Keep overage
  4. This overage will be recognized as revenue and will show on the Group Sales Revenue Report as well as other revenue reports, like Total Revenue Report. 
Note: You can only keep an overage for reservations that are checked in and made after February 2013 (v.2.96) release of Altru. Overages can also be mapped separately in the General Ledger. See this solution on how to map this in the GL.