Start by putting tape around the area that you want to patch. This will keep the wood filler from getting all over the rest of the floor. If there is anything down in the floor like dog hair or crumbs make sure you get that stuff out before you put the wood filler in the area. Then take some wood filler in a plastic tube and put a line of filler in the hole. Use a putty knife to force it down into the area you are filling and then scrap the excess off. Do this until the hole is completely filled. Then remove the tape and let it completely dry. If you have pets you might want to put a plastic bowl over the spot until it is dried. Make sure you tape the bowl down until it is dried so that the bowl will stay in place. This is a very easy fix that will prevent you from calling for an expensive repair.