If your iron has already been tinned, you can simply flow new solder onto it and wipe it off with a clean rag. If for some reason it hasn't been tinned, you may have to get a little more aggressive and use a Scotch pad or 220 grit paper. Clean it up really good (no fingerprints), and then go about tinning it. An untinned iron will not solder. As noted above, cleanliness is very important. Jim