This is an excellent assignment. Of course, your starting point is to realise that the story would completely change out of necessity. Part of the success of the original story is the way that the interior monologue of the unnamed barber hides a crucial fact from both him and us which is only revealed in the final paragraph. The fact that Captain Torres had always known about the barber's connection with the rebels completely changes our opinion of him and of all that we have read prior to that.
Telling the story from the point of view of Captain Torres would probably make us appreciate his bravery even more. Remember that first-person narratives are always partial, because they only see the action through the eyes of one character. Captain Torres would not have access to the thoughts of the barber, he would only be able to see the barber and interpret his body language. I wonder whether the barber's attempts to hide his emotions that we are shown in the original were successful. Of course, as the original goes through the thought processes that cause the barber not to kill Torres, you would likewise need to capture the uncertainty and perhaps fear of Torres as he is shaved by the barber and knows that any moment could be his last. You would also have to perhaps explain more fully why he walks out without doing anything. Good luck!