Vinegar works great, let soak for a while. You do need to rinse the vinegar out of the iron after it has soaked long enough to release the lime deposits.

Hold the hot iron over the sink (don't touch sink) and use the button for puffs of steam repeatedly. Fill with clear water and do the same repeatedly until no more junk comes out.

Test ironing on fabric you don't care if it gets ruin to see if the iron is clean and no more junk to spit out.