Cannot merge conflicts for an approved pull request

[Hanntz Fourkijn]

My pull request containing conflicts was approved. When I click on "More Information" after the conflict warning, the following dialog pops up:

 This pull request has conflicts. You must resolve the conflicts before you can merge:

Step 1: Fetch the changes (saving the source branch as FETCH_HEAD).

git fetch origin Feature1

Step 2: Checkout the target branch and merge in the changes from the source branch. Resolve conflicts.

git checkout uat
git merge FETCH_HEAD

Step 3: After the merge conflicts are resolved, stage the changes accordingly, commit the changes and push.

git commit
git push origin HEAD

Step 4: The pull request will be updated and marked as merged.

I have done all steps, but the last one in #3. When I push, I get the following error:

remote: Branch refs/heads/uat can only be modified through pull requests.

remote: Check your branch permissions configuration with the project administrator. 

What is the correct command to complete the pull request merge?