A vet can be helpful if they are familiar with bumblefoot, but in the meantime and in any case,
You can do several things.
First, make a compress with Epsom salt and water solution. Add a couple of tablespoons of E.s. to a half cup of warm water, soak a clean cloth in it, and wrap each foot and leg in the cloth for about five minutes.
Or, increase the amount of solution a bit and put it in a flat-bottomed bowl or very small bucket and have the duck stand in this for five to ten minutes.
After soaking, put a few drops of clear iodine on the bumble. Make sure it dries before putting the duck down. After three to five days, soak the feet again - perhaps just letting the duck swim in a lukewarm tub of water, to loosen the scabs on the feet and then gently see if you can tug the scabs and pull some of the yuck out of the foot. If all the pus (which is more like a chunky material than liquid) does not come out, repeat the iodine treatment.
If you don't have clear iodine right now, then slather the soaked feet with triple antibiotic ointment (without painkiller).
If the legs are warm, you may need an oral antibiotic as well, because the infection may have started to spread.
Here is the post from Haunted55 when she discovered the clear iodine treatment.
On July 1st, I found one of my Pekin ducks with what I would consider a bad case of Bumblefoot. Both feet were involved and I'm ashamed to say, the only way I found it was she was limping. One foot had 7 and the other had 3. I was able to grab her and bring her into the house and put her into a warm bath to clean and soak. Two water changes later and softened feet, all I had time to do was paint the bumbles with colorless iodine, grabbed the wrong stuff, and put her into a dog crate in my house until I could get everything ready to operate and get them gone. Did I mention the thought of this scared me half to death?
Sad to say it took 6 days before i was able to get everything together and someone to help out with the 'cure'. The following pictures are what we found after the bath we gave before the planned surgery to remove these things.
As can be seen, there really wasn't much to operate on, even though I was prepared to do just that. No matter how much squeezing or prodding or soaking, there just wasn't anything more to come out, it was all on the scabs that were covering the sores. The swelling was down from the 'marbles' I saw when I first found them. I poured betadine over the ones I had opened and painted the ones that I hadn't again with the iodine and put her back into her crate with clean bedding.
the next pictures are of the same Pekin and anothe duck, Dottie the Mallard, who was also found limping.
As can be seen in the first two pictures, the bumbles have been dramatically reduced on the Pekin with just the iodine application and the smaller ones totally gone. The last four pictures are of the Mallard who is still under going the iodine applications.
As can be seen, this is how the left and right foot look tonight on the Pekin duck. The heels being the worst are still showing infection and need for more treatment. tomorrow, I will again give a bath and pull/cut out the scabbing and treat with straight iodine this time. These spots are now flat or as flat as they should be considering the part of the foot they are on. I will still touch up the places that had the spots before as well.
I got clear iodine at Walmart, by the way. Epsom salt if you don't have it, is sold at most drugstores and grocery stores. It is inexpensive, as is the clear iodine, and very useful to keep on hand.
It is a laxative, do not let the duck drink the Epsom salt water.