If it's anything like my recliner, the bolts go through the floor. The bolts were near the passenger front wheel well and simply held in place by washers and nuts.
My recliner started to wobble and was leaning to one side. I realized that they had installed the chair after the undercoating was applied, meaning about 1/2 inch of undercoating was between the washer and the floor. After a while, the coating around the washers on one side eroded and the chair was loose. Unfortunately, the bolts were so badly corroded, I was only able to back them off about an inch. I had to then cut them off and install new ones.
Depending on what is under your sofa is where you will find the other end of the bolts. My sofa is on the slide room and I know the bolts are not exposed under the slide. Either the nuts are into a threaded hole (hopefully), or the nuts are somewhere between the floor and underside of the slide room.
'03 41' Friendship & 24' trailer with HIS '03 H-D Heritage Springer, HER '15 H-D Freewheeler Trike, and '08 Smart Car.
"Adventure is found in the journey, not the destination."