How can I treat popped burn blisters?

You describe a 2nd- ...Degree or partial-thickness burn that will heal on its own, given good wound care. Keep the wound clean and apply antibiotic ointment to it until healed. Use simple pain meds, such as Ibuprofen or Acetaminophen for discomfort. If it does not heal or seems like it's getting infected, you should seek medical care.