You activate the Bonfire that allowed you to cure Kodlak while you have another Glenmoril Witch Head in your inventory. It will summon another spirit wolf you have to kill.

To cure yourself, activate the Flame of the Harbinger (making sure you have at least one of the Glenmoril Witch heads in your inventory) and then kill your wolf spirit. This is the same place you cured Kodlak during the Companions quest "Glory of the Dead". Sometimes you may not be able to cure yourself, if you have not yet cured Farkas and Vilkas during their "Purity" quests. Finishing both "Purity" quests should allow you to cure yourself of beastblood (as explained above).