If your changes have merge conflicts with the base branch, you must address the merge conflicts before you can merge your pull request's changes.

About merge conflicts

Git can often resolve differences between merged branches. Usually, the changes are on different lines, or even in different files, which makes the merge simple for computers to understand. However, sometimes there are competing changes that Git needs your help with to decide which changes to incorporate in the final merge. Often, merge conflicts happen when people make different changes to the same line of the same file, or when one person edits a file and another person deletes the same file. You must resolve the conflict before you can merge the branches.

Resolving a merge conflict on GitHub

You can resolve simple merge conflicts that involve competing line changes on GitHub.

Resolving a merge conflict using the command line

You can resolve merge conflicts using the command line and a text editor.