Add and remove group members in Outlook - Microsoft Support
Open Outlook for Windows. Under Groups in the left folder pane, select your group. On the Groups ribbon, select Add Members. In the Add Members box, search for people within your organization either by their full name or email address, and then select the names to add. Click OK.
Applies To:
Outlook for Microsoft 365, Outlook for Microsoft 365 for Mac, Outlook 2021, Outlook 2021 for Mac, Outlook 2019, Outlook 2019 for Mac, Outlook 2016, New Outlook for Windows, Outlook for iOS