If you need to access another user's OneDrive for Business site or need to grant someone else access to another user's OneDrive for Business site (such as assigning rights to a manager after someone leaves the organization), you'll need to manage the site collection owners. By adding a user as a site collection owner, you are granting full access to all the files and folders in the site. Follow these steps to assign ownership:
- Launch the User Profile Service application from the classic SharePoint admin page.
- Under People, select Manage User Profiles.
- In the Find profiles box, enter the name or address of a user to manage and click Find.
- Hover over the user. When the down arrow appears on the user, click it. Select Manage site collection owners:
- Under Site Collection Administrators, add the names of the additional users that you want to grant full permissions to. Click OK when you're finished:
The owner of the site collection is listed by default in the Primary Site Collection Administrator and Site Collection Administrators areas. A site can only have one primary site collection owner but can have many secondary site collection owners.
Now that you have granted the additional user site collection administrator permissions, your users should be able to access the site.