The soldering iron tip will be very hot! Be careful when handling the soldering iron during its operation.

Hold down the damp sponge.

Use a damp sponge not a wet sponge so it won't burn. Also make sure the sponge is made from a cellulose material not a polymer. You don't want the sponge to melt and mess up your iron.

While the soldering iron is hot, use a rubbing motion across the sponge to remove excess solder off the soldering iron tip.

When you have cleaned the iron, melt a small amount of solder on it to "re-tin" the tip.