Assigning issues and pull requests to other GitHub users

On GitHub.com, navigate to the main page of the repository. Under your repository name, click Issues or Pull requests. Select the checkbox next to the items you want to assign to someone. In the upper-right corner, click Assign. To assign the items to a user, start typing their username, then click their name when it appears.

https://docs.github.com/en/issues/tracking-your-work-with-issues/assigning-issues-and-pull-requests-to-other-github-users