They say if you can see the "bump", you should soak it 20 minutes in epsom salt warm water, then attempt to "pull" the scab to hopefully drain infection. Following this you should use antibiotic ointment and bandage the foot.
While we treated our duck, we kept her in a dog kennel. She was alone at first and miserable, constantly calling for the flock of 5 friends. Finally we put a drake in with her and she calmed down. She stayed in the cage 2 days, then pulled off all the bandages. We didn't re-soak/re-treat the foot because the scab would not disengage. We are watching her closely and checking for the bump to turn black. If it does not, I will not interfere with her again.