In order to get soot out from a sofa, the best method would be a two-fold approach. One would be to apply something that would absorb the soot from the stain. You can leave a thick layer of corn starch or baking soda on the stain for at least a couple of hours to do this. Leave it on overnight for it to work best. Dry cleaning solvents are easily available in the market, and the best thing to use for soot stains. Once you rub off the baking soda or corn starch, then you should rub the solvent into the area and let it work for a few minutes. Once the stain has lightened considerably, you can blot it off the sofa. If your stain is a long-standing one, this would be the most effective way to work on it.
For a relatively fresh stain, you can use a stain remover, once again, easily available off the shelf and rub it into the garment. Leave it on for about 15 minutes and then launder the fabric. If you have the kind of upholstery that does not come off the sofa, then you can simply use a clean wet cloth and rub until the stain disappears. Vacuum the sofa after you have done this to remove all traces of the stain remover and water.
answered by G M