You can use a disposable scalpel blade to lance it. First clean the skin with betadine, and after lancing, squeeze to try and get all the pus out. Clean again, apply some plain neosporin ointment, and a 2x2 gauze. Then wrap with vet wrap strips, but not too tight. It is always best to have everything laid out and ready, then get a spare pair of hands. Wrapping the bird in a towel can help to keep them calm. Here is an article with a video:
https://www.hobbyfarms.com/how-to-treat-bumblefoot-in-chickens-3/
https://www.hobbyfarms.com/how-to-treat-bumblefoot-in-chickens-3/