If you need to grant a user or group standing access to a user's personal sites, you may want to consider assigning a secondary site collection admin. To set a secondary site collection owner globally, follow these steps:
- Navigate to the SharePoint admin center Classic Features administration center (https://admin.microsoft.com | Admin centers | SharePoint | Classic Features).
- Launch the User Profile Service application from the classic SharePoint admin page by selecting User profiles.
- Under My Site Settings, select Setup My Sites.
- Scroll down to My Site Secondary Admin.
- Ensure the Enable My Site secondary admin box is selected. Then, add a username or security group through the user picker:
- Scroll to the bottom of the page and click OK.
This change only affects OneDrive for Business sites that are provisioned going forward. It does not impact existing sites.