This is for if a user cannot access their own onedrive due to them not having permission to access it.

  1. Go to SharePoint Admin Center > Manage User Profiles

2. Look for the affected user right click over the profile and click on “Manage site collection owners” 

3. Remove the user from both fields (Owner and Site collection Administrator) and set temporarily your Admin account in both field. Click on the person icon in both field to confirm that the new UPN’s are correctly input. 

4. Access his personal site replacing the last part of the URL as follows: <OneDriveURL>/_layouts/15/people.aspx?MembershipGroupId=0 

5. Delete the affected user from this “People and Groups” list

6. Repeat the steps 1 to 3 but this time set the user back as Owner of the Site