Look, everyone knows that in that kind of scenario, there would be a secret high tech enclave, probably worshipping the great god NASA (or ELON for modern audiences) who have been literally religiously maintaining a space going vehicle of some kind throughout the Event and the post-Event “Unpleasantness”, etc.
Together of course with all the necessary infrastructure and equipment to get to the moon and back and recreate all the species from the centuries old data and samples on the Moon.
Therefore all our hero needs to do is escape the marauders, make it to the enclave, persuade them he is the awaited Techno-Messiah and/or steal the Upgoer.
