Manual steps to decrypt a file?

I'm using a CI build that downloads a zip archive from github. At build time, I need to decrypt a file that has been encrypted with git-crypt using gpg. However, the CI build cannot decrypt the files because it is not a cloned directory tree and thus I cannot run 'git crypt unlock'.

I see the .git-crypt tree, but what are the manual steps to gpg to decrypt a file?

Any guidance appreciated.