You can configure pull request merge options on GitHub.com to meet your workflow needs and preferences for managing Git history. For more information, see "Configuring pull request merges."
On GitHub.com, navigate to the main page of the repository.
Under your repository name, click Settings. If you cannot see the "Settings" tab, select the dropdown menu, then click Settings.
Under "Pull Requests", select Allow merge commits. This allows contributors to merge a pull request with a full history of commits.
Optionally, under Allow merge commits, use the dropdown to choose the format of the commit message presented to contributors when merging. The default message includes the pull request number and title. For example,
Merge pull request #123 from patch-1. You can also choose to use just the pull request title, or the pull request title and description.
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."