To treat mild cases of bumblefoot, I wipe the duck's foot with a few drops of povidone iodine (betadyne is one brand) in a few tablespoons of water to clean it; I smear some triple antibiotic (Neosporin is one brand) on the foot. Usually I do this at night, then a time or two during the day. I have covered the foot with a bandage at night in a few cases, but usually a regular application of the ointment, which is greasy, seems to help.
It takes several weeks for it to completely heal (I catch it early, or at least so far I have), but improvement has been seen within days.