How to pull changes in pull-request from upstream if the fork is not available due to privacy?

Question

git

Good evening.
There is a private repository that has several forks. I see only the number of forks and my fork, for some reason I don’t see other forks (I suppose there are not enough rights, perhaps every owner of a private fork should grant me these rights). Pull requests are pouring into the private master.

The task was to deploy and test the pull request locally. But there were serious difficulties with this. What I found on the Internet, and what should work, does not work for me. Something is being pumped out, but at the same time, in the created test_pr_branch there is always some kind of left commit that has nothing to do with the desired PR. I don't have access to the original fork branch. How to download PR for local tests if the fork branch is not available?
git pull upstream pull/<ID>/head:test_pr_branch