GitHub has the ability to set the default reviewer using a CODEOWNERS file.
Code owners are automatically requested for review when someone opens a pull request that modifies code that they own. When someone with admin permissions has enabled required reviews, they can optionally require approval from a code owner.
To use a CODEOWNERS file, create a new file called CODEOWNERS in the root,
docs/, or.github/directory of the repository, in the branch where you’d like to add the code owners.