Stay away from chemicals if possible. They are not necessary, get a file or knife and a moist sponge. Heat the Iron and have solder handy. Get a molten ball of solder on the tip of the iron and file or scrape the black region wipe on the sponge, keep scraping in the presence of solder until you get to the bare metal underneath, clean frequently on the sponge. It may take a few minutes but you should be able to get the entire tip of the iron wetted with solder this way. In the future all ways put away your iron with a ball of solder on the tip, first thing after heating it up wipe it clean on the moist sponge, keep the tip clean when using it by frequently tinning it and wiping on the sponge. Between solderings (?) leave a moltan ball of solder coating the tip, wipe clean and rewet before using.
When I was a Electronics Tech in the Navy my chief used to say "Tin it all the way to your elbow!" That means tin as far up the tip as you can, not just the soldering point.
Good luck