Restoring Gitlab back-up into new instance (total amateur)

I have a new project from which I need documentation from an older Gitlab instance. Our server was shutdown in the process and so I have only the back-up file to go on (v 12.9.2-ee). I am a complete novice to Git. I’ve managed to install locally on Windows and run commands that attempt to load the back-up .tar file into a new account I created. When I attempt to do this in the browser, I eventually receive a Page Not Found error. When I attempt through bash/CMD, I eventually receive a 502 Bad Gateway error. I suspect it’s largely due to a version mismatch, but I cannot find the same version in these old runner pages. Because what I need is only a subset of the 3.7GB .tar file, I tried unzipping it and running unbundle on the specific bundle files, but I also received version errors there.

I don’t know where to go next. I am sorry that this is such a beginner question, but I’m rather stuck and I really only need access to these files for 12-24 hours while I extract for requirements documentation.

I was using this command in bash and CMD, to no avail: curl --request POST --header "PRIVATE-TOKEN: XXXXXXXXXXXX" --form "path=api-project" --form "file=C:\Users\LOCAL\Downloads\1607648505_2020_12_11_12.9.2-ee_gitlab_backup.tar" "[]("