My dog has a popped bump on his paw. What is it and how to treat?

Given Rambo's age, it is less likely that he has a growth or mass of serious concern. However, without a fine needle aspirate or a biopsy of the lesion it is impossible to know. Given its appearance in the pictures, it looks like it was likely either some type of tumor or cyst that underwent too much pressure from fluid build up, and subsequently ruptured. In terms of treatment, you are doing most everything you can at home already. Some recommendations though:
I would not use peroxide as this can actually delay the healing process
I would not keep the area covered too closely or tightly as this can encourage reinfection
I would instead place a cone or collar on Rambo to prevent licking or self-mutiation, as this still allows the area to be open to the air.

In terms of what to do next or how to find out what you are seeing, you can do two different things. The first is simply wait and see what happens when the area heals. If it never grows back, great new! The second option would be to take him to the vet and try to obtain a sample for analysis. You can also wait to do this if you want when and if the lesion grows back.