While I have found uses of "report about" on the internet, neither oxford nor cambridge dictionaries recognise it. If you want to replace upon with something different, I can only see a case for "report on"
That said, i believe "report about" vs "report upon" is a big change in the meaning behind the phrase. Report upon just implies that you need to contact the president after getting the number. Report about implies that you need to literally report to them the fact that you now have the number. In my opinion, when they say "report to the president upon receiving the number" they don't really mean that you need to go and tell them that you got it, but rather that you should go see the president once you have it and get further instructions there. I hope it was helpful for those who learn english.
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