Do not wait! A little extra heat will not cure a serious RI. It sounds like the snake is in an intermediate/advanced stage. Return the animal asap or take it to the vet and get a culture done. But it's not really cheap to treat an RI. And antibiotics will not make your snake any worse. Just the same or better.
The guys who shipped the snake sounds very unprofessional and not very knowledgeable .
Take pictures to document the injury as well. And maybe a video showing the wheezing and bubbles.
Good luck.
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