Hi Ankriti,
If you have your change on a branch and its just one commit, you could do the following:
git checkout ucr
git pull
git checkout BRANCH
git rebase HEAD~1 --onto ucr
This should move your commit onto the latest version of the ucr* branch. You should then be able to submit this branch as a pull request with ucr as the base branch.
Cheers,
Evan
* ucr is the branch for any changes that affect the companion behavior.