Wrapping a webbed foot is a challenge, and ducks worry at things till they come off, most of the time. Some do well with moleskin, a bandaging with a sticky side. Others of us have done okay with vet wrap or baby socks.
I prefer to try to treat with topical at first, because opening a wound increases risk of further infection. At the same time, if the infection is already well along, it may be advisable to do surgery.
Try 3x a day ointment on the top and bottom of the foot and see if it improves. But I would not wait more than that to decide if cutting is needed. If it needs cut, then the duck needs to stay in sick bay until the cut is healed over, and I am guessing that would be two or three days.