Welcome to the forum. Sounds like a nasty problem. If I understand it correctly......flooring plywood pieces meet along the top of a floor support bracket underneath, but there are no screws securing the flooring plywood pieces to the brackets and the flooring wood has lifted.
One suggestion might be to install a couple "metal inserts" into the plywood flooring on either side of the flooring support bracket, “carefully” sized not to come through your flooring topside. (Hope they used 3/4" plywood decking but you need to make sure). Then use a strong metal bracket strapped across the underside of the flooring support bracket and bolt that cross bracket into the flooring threaded inserts at both ends. If you did that in a couple strategic locations along the high spot you might be able to pull the lifted area back down onto the top of the coach flooring support bracket. Of course choosing and installing the correct threaded inserts into the flooring plywood would be “no fun” from below, and you would need to match the bolt length used to pass through the added cross brackets to the depth of threaded inserts and amount of “pull down” required to re-level the floor. Bending ears onto the cross bracket might be required to adjust that tightening depth adjustment. This is probably about as clear as mud?
The other option is using a "wood threaded dowel screw" instead of the inserts. Threads into the plywood floor below like a wood screw, but has a threaded half that you could use a matching nut on to suck the floor down to the cross brackets noted previously. Others may have better fastener and adjustment suggestions.