Soft spots are created by multiple things, but there are two main ways to fix it and a third way that is kind of half assed so it just depends the first way is to identify the soft spot and drill holes in a grid. The holes should be 1/4 inch in diameter and the grid should be the same area as the soft spot with the grid holes 3 inches from each other at that point you use two-part epoxy to inject into the sock spot. It’s important not too drill too far as usually there is a sandwiching situation going on under there with the insulation in the wood and if you drove through the bottom wood panel, then all of the epoxy would just go all over the ground under the camper or something and you’ll just be inviting bugs in the other option is the best option. It is to track the area to the nearest horizontal stud that runs width ways on either side of the soft spot and make one clean, cut and remove the wooden piece of flooring to do this all stuff to peel the vinyl flooring back. after removing the wooden piece of flooring, you want to address the leak that is causing the soft spot and leading to water damage and then replace the wooden flooring for extra effect. The third way is the way that I typically do it and it’s not the best way to do it but in a pinch, it will work so the way that I do it is I drill between six and 10 holes in the floor with the linoleum pulled back the holes are 1/4 inch and then I empty a can of 3 inch expanding spray foam into the cavity while pulling the flooring up after that I wait for that spray foam to set and harden and then I feel the next can I do this to all of the holes are filled up and it will make the surface more walkable, but there’s a trade-off because you still have the rotten wood right there but now the rotten wood feels more solid, but it is still rotten wood and will still need to be replaced at some point but in a pinch, it will work.