my advice is to write this scene in the first person, because it’s the best way to truly experience the immediacy of what’s happening from your protagonist’s point of view. In fact, even if you are planning to write your novel in the third person, I would advise you to write every backstory scene in the first person—whether it’s your protagonist’s backstory or that of a secondary character. You can switch back to third person when you start writing the first scene of the novel itself.
