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" "[]("

It appears that you are trying to post a self-managed instance backup file onto a project address. This will not work.

Instead, try installing GitLab 12.9.2-ee on a local Linux VM by following this: Manually download and install a GitLab package | GitLab

Then, once it is done, follow this guide to restore your local backup file over it: Back up and restore GitLab | GitLab

After this you will be able to browse the older projects from the UIs within.

Alternatively, if what you need is available in just the repository portion of the backup data, you can extract just the relevant repository bundle file from inside the backup repo, and clone from it: