By committing the code to a git repo and having a code review like every other language out there.
I'm guessing you have never tried these things but image based Smalltalk implementations have supported VCS for decades now, literally. In Pharo this is with git using Iceberg:
It's not magic, it's not even a problem, because the problem you're imagining doesn't actually exist. So long as the user of the system has at least half a brain (and maybe less) they will be capable of distributing their code with git these days.
I'm guessing you have never tried these things but image based Smalltalk implementations have supported VCS for decades now, literally. In Pharo this is with git using Iceberg:
https://github.com/pharo-vcs/iceberg
They even wrote a tutorial to make it easier: https://github.com/pharo-vcs/iceberg/wiki/Tutorial
It's not magic, it's not even a problem, because the problem you're imagining doesn't actually exist. So long as the user of the system has at least half a brain (and maybe less) they will be capable of distributing their code with git these days.