How to resolve merge conflict in pull request in VSTS?

I've created pull request I got into this:

"Approve" button does nothing and complete is disabled.

How do I resolve this confligt in pull request?

Update

Microsoft just added browser based merges. This may get you out of a pickle for small conflicts.

And offers improved visualizations of the different scenarios as of Sprint 150.

For more complex situations:

You have two options to resolve the conflict, reverse-integrate the changes from the target branch (which creates additional merge commits), or rebase on the target branch (which leaves your history nice and clean).

---

Merge from target to current branch prior to completing the PR.

You need to clone the repo locally, perform a merge from the target branch to your branch and push those changes up to the repository. VSTS will detect the changes and update the pull request.

            -------o3              PR
           /
---------o1-o2                     target

Thus merge target (o2) to PR:

            -------o3-o4           PR
           /          /
---------o1----------o2            target

Then complete the PR

            -------o3-o4           PR
           /          / \
---------o1----------o2--o5        target

---

Rebase the PR branch to include the latest changes on target

Alternatively, you can clone the repo locally, rebase the PR branch on the latest version of the target branch, solve all issues from the rebase and force-push the changes back to the PR branch. VSTS will detect the changes and update the pull request.

            -------o3              PR
           /
---------o1-o2                     target

Thus rebase o3 onto o2:

              -------o3            PR
             /
---------o1-o2                     target

Then complete the PR (with Fast-forward merge in the case below):

---------o1-o2-o3                  target

1. Open your project with Visual Studio.
2. Open View > Team Explorer
3. Change to Branches tab.
4. Double click to the branch you intend to merge (e.g. dev).
5. Right Click > Merge From > Select
   Merge from branch: master,
   Into current branch: dev
6. Click Merge button
7. Choose the conflict file(s)
8. Then resolve the conflicts. You can click the left or right checkbox for the section you want to include.
9. Then commit the merge
10. Done.

To answer @metabuddy's question: >And then what? This only shows how to resolve conflicts locally, I can't push the target nor source branch directly to VSTS because I have branch policies which require pull requests to be made from feature branches.

You can follow the steps above. Just the source branch and target branch will be slightly different.

1. branch merge from: master
2. branch into: your-feature-branch
3. Create Pull Request to merge from your-feature-branch into master

You could do the above technique by @jessiehouwing or use the new plug-in. MicrosoftDevLabs released the link to the plugin to resolve conflicts. The link to plugin is given below https://marketplace.visualstudio.com/items?itemName=ms-devlabs.conflicts-tab

This answer is in reference of comment by @metabuddy on the answer of @sky91

What if your target branch in 'master' and on 'master' branch you have the policies applied to not accept direct merges?

Note: Consider 'master' is target branch and 'x001' is the source branch in pull request, which has conflicts between 'master' and 'x001' branch.

In that case solution by @sky91 will not work. For this you to follow these steps.

1. Create a new branch from target ('master') branch, like 'x002'
2. Go to visual studio, and select 'x002'
3. Merge 'x002' from 'x001' branch.
4. Go to your pull request and change the target branch to 'x002'
5. It will show the same conflicts as you have in the pull request.
6. Resolve all the conflicts and commit the merge.
7. When you refresh the pull request page, it will show that 'changes already merge'
8. It must show 'Close' button. if it is there, then close this pull request.
9. Now all your changes has been merged and saved to 'x002'
10. Create a new pull request from 'x002' to 'master'
11. Because all the conflicts are gone, it will allow merging into 'master' branch.