Using GitHub Enterprise, I forked a private repo. I then made the upstream repo public, which broke the 'fork' relationship between the public upstream and my private personal fork (as noted here). I've now also made my copy of the repo public. As far as I can tell, I can no longer make pull requests from my copy of the repo to upstream, because my copy is not recognized as a fork of upstream.
Can I re-associate my repo with the upstream repo as a fork?