I should have taken pictures.
To install the seatbelts you have to remove the plastic covering. There are two screws. The middle seat is easy, Just pop passenger seat up (it folds forward to allow passengers to get into the third row), then remove the two screws, then the plastic trim comes off. I think it uses a T45 or T50. An allen wrench probably works in a pinch. Keep your hand on the seat belt and pull out the bolt. You'll see that there is a spring and washer inside that pushes the seatbelt back down into place. Study it a bit before you remove it, then replace it with the correct part number (they are technically different; the middle one doesn't have a notch inside) with the spring in the correct place. Then go sit on the drivers side and you should be able to access the passenger side screws (still folded forward for access). The side plastic piece doesn't come off as easily, and it doesn't go back in as easily. There are some internal plastic pieces that you will likely break. Continue with the same procedure and then put it back into place. That's it. Should take about 30 minutes.