I am trying to replace the speedometer gear, where is it located?

1996 Isuzu Rodeo 2 WD V6 3.2L mileage: 39,000. I am trying to replace the speedometer gear, but I'm not sure where on the transmission this item is located and how to install it. Please help! Help! Help! My speedometer is not operating and just sits on 0. The dealer's rep. Said that it was the speedometer gear and that it would take about 5 minutes to install. Please respond ASAP. Thank you.