Now you can merge their branch to your local branch. But before you do this, I recommend you create a new branch first and do experimental stuff on top of the new branch so you won't mess with the master branch:
The following example is not directly related to Git, but exclusive to GitHub, although Bitbucket, GitLab etc. tend to provide similar mechanisms.
First, you have to figure out the PR number. It'll be prominently listed on the PR page as well as in the URL. As an example, we'll take `#6282`. Now you can fetch and checkout that code using the GitHub-specific reference:
```bash
git fetch upstream pull/6282/head
git checkout FETCH_HEAD
```
Once you've finished testing, you can just `git checkout master` and it'll be as if nothing ever happened.
How to submit my change on top of current development (which is master branch at origin).
This assumes that your repository clone have `origin` which points to upstream official repository as shown below. If you did checkout from your forked copy, and origin points to your local fork, you can always add another remote and replace `origin` in this instructions with another remote name.