You can configure pull request merge options on your GitHub Enterprise Server instance to meet your workflow needs and preferences for managing Git history. For more information, see "Configuring pull request merges."
For information about the default commit messages for squash merges, see "About pull request merges."
On your GitHub Enterprise Server instance, navigate to the main page of the repository.
Under your repository name, click Settings.
Under "Merge button", select Allow squash merging. This allows contributors to merge a pull request by squashing all commits into a single commit. The default commit message presented to contributors when merging is the commit title and message if the pull request contains only 1 commit, or the pull request title and list of commits if the pull request contains 2 or more commits.
If you select more than one merge method, collaborators can choose which type of merge commit to use when they merge a pull request. If there is a protected branch rule in your repository that requires a linear commit history, you must allow squash merging, rebase merging, or both. For more information, see "About protected branches."