Q:

How to submit a PR against a now-broken upstream?

I'm a Git(Hub) neophyte.
I forked, changed and submitted a PR against a GitHub repo (R'). The PR has not been reviewed|accepted.
Meanwhile I wanted to submit a separate (non-overlapping) PR and followed instructions here to create a 2nd copy of the remote repo in my GitHub account (R").
I wrote the code and committed the changes to it (R") but I'm unable to submit a PR using the GitHub UI.

Am I screwed?
Or is there a way I can add back the original origin so that I may submit the PR?
I Googled around and tried:
git remote add upstream https://github.com/GoogleCloudPlatform/cloud-builders-community.git
But that made no difference.
Any guidance would be appreciated!

A:

You shouldn't need to "fork" twice: from the local clone of your first fork, you can simply 

create another branch (from upstream/master), 
make a second patch in that branch, 
push that second branch
make a second PR from said second branch on your GitHub fork.

