WARNING: This page is about a different car, the 2013 Honda Odyssey, 2012 Honda Odyssey, and 2011 Honda Odyssey. However, it is still accessible from the selected car via links, so may be relevant.
Remove the reverse idler gear assembly (A) from the transmission housing.
Fig 1: Reverse Idler Gear Assembly And Dowel Pins With Torque Specifications
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Install the reverse idler gear assembly with the two dowel pins (B) in the transmission housing.