It’s not too difficult to understand the steps to follow to make this repair the best way, but it will definitely be messy and can be heavy work. You’ll probably want to get a helper—preferably someone with a little drywall experience. First, cut away the damaged drywall and remove any wet insulation. If the studs are stained and not rotted, wash them with a diluted bleach and water mixture, then coat them with an antimicrobial solution that your hardware store sells in spray bottles. If the studs are rotted, you will need to cut them out and install new ones, one at a time. Then replace any damaged insulation. If the flooring you’re referring to is the finished floor surface, you’ll probably want to replace or refinish the whole room to get it to match. If it’s the plywood sub-floor that’s rotted, cut out the bad section, ending on the center lines of floor joists where the subfloor is still solid, then piece in a plywood patch of the same thickness and screw it tightly down to the floor joists, including the ones around the perimeter where the patch shares the joists with the original floor. Then finish the walls by patching in new sheets of drywall, taping, and mudding the seams. Then prime with PVA primer for new drywall, and paint.
