If you have found that you can't replace the wood the legs screw into, try a few bricks or cinder blocks under the couch if the couch is able to hide them. We had to use cinder blocks for a few months once when we couldn't afford to replace the legs, it works but its ugly.
Put something in the holes that the screws can bite into. Like pieces of wood. In a small hole, I have used wood matchsticks, without the heads of course. Or try wrapping the screws in gray tape (a lot) and then screwing them in. Hope that helps. TC in MO
If you mean the holes you screw the legs in to the sofa are oblierated all you have to do is get some heavy duty carpenters glue, turn the sofa upside down, fill the holes about 3/4ths of the way with the glue, put new screwable legs in, allow to dry for a full day or two and "Voila" ;-)
Even if it isn't a sofa that originally had screw in legs you can simply purchase new feet and glue feet to the part the original ones were ;-)
When I was young I used four bricks as feet so that the sofa would be up off the floor ;-)
You might find some legs at Lowe's or get a carpenter to make some or get a 4x4 lumber from Lowe's, cut & trim to make the legs as tall as you like. Attach them to couch with glue or screws. Then put varnish or paint on them to match the couch, good luck.
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