poultry09, please don't feel bad about not noticing. It's tough to catch on to everything that is happening with a duck, and one you aren't familiar with yet.
Penicillin can be given orally or by injection. Even if the vet can give you an idea of what kind of antibiotic would be best, that would be a help.
Unlike many cysts, bumble foot's inner yuckiness has been described on the forum as a cottage cheese consistency, so lancing would not make enough room for the material to come out. So a slit would need to be cut in the foot.
Now, if it's not done properly the cutting can cause a bunch of bleeding, and there is the risk of additional infection if the wound is not kept clean enough long enough after cutting, and with a duck, hooooo, wee, it can be tough to keep their feet clean. It involves wrapping the foot. It can be done, it is far from impossible, and it is a real learning experience!
Many of us have done well with lots of soaking, lots of topical antibiotic, and time and patience.
Here is a topic posted to show how one person deals with bumble foot on a chicken:
https://www.backyardchickens.com/t/236649/bumblefoot-surgery-with-pics-and-how-to
newbyduckmom just had to go through the surgery. Again, you may not need to or want to.
https://www.backyardchickens.com/t/617479/bumblefoot
And it takes a while for the healing to finish.