I don't think a plus one seat was made until 2005.
behind driver and passenger seat under the carpet
The eighth seat needs to be folded properly according to the Odyssey specifications. When folded properly lift the floor storage area and the seat will slide in.
Behind the seat.
To remove the back seat from a 1997 Honda Odyssey the seat locks need to be opened. When the clips are unlocked the seat will be able to be lifted up and removed from the vehicle.
The 2005 and newer Odyssey have a center seat that is 1/2 the size of the other seats. There is nothing available in the early models in the way of a third seat.
On the 2006 Odyssey first remove each seat headrest and fold the seat in half. Then reach under the seat bottom and release the black lever that is closest to the outside doors which will unlock the rear floor clamps. Tilt the seat forward, slide the seat backward to release the front clamps and lift. Careful it is heavy.
look on Honda websites
It is located under the driver's seat.
There are latches that hold the metal seat frames to the floor. You can use a screwdriver to open them.
You should not try to install seat belts yourself, it says so in your owners manual. Plus it is dangerous, because if you don't do it properly, you can kill anyone sitting in that seat. Take it a professional, A seat belt equals life!
Put on your seatbelt!
There is dvd drive under driver seat