OneDrive for Business retention and deletion

Their OneDrive for Business will be preserved for 30 days. You’re the temporary owner of all documents saved to their OneDrive for Business.

Reason

When a OneDrive for the Business site collection is scheduled for deletion, the default action is to transfer ownership of the site to the manager of the original work account or school account that is being deleted. For this to occur, the user profile Manager Property must be set for the original owner of the OneDrive for Business site. For more go to OneDrive retention

For this to occur, the user profile Manager Property and Access Delegation need to be set for the deleted user before deleting it. To do that, as a global admin or SharePoint admin, please follow the steps below: 
1. Go to the SharePoint admin center. 
2. Click User profiles > People > Manage User Profiles > Find the user account to deleted > Edit my profile > Manager > type the manager account into the box > Save and Close. 

Go to central admin

Then Edit my profile

Make sure the manager is there

 Go to SharePoint admin center > User profiles > My Site Settings > Setup My Sites > My Site Cleanup > tick Enable access delegation> Secondary Owner as below:

Access Delegation option in the central admin
must be enabled

Now as a manager or secondary owner you will be able to access when you receive the Email

Their OneDrive for Business will be preserved for 30 days. You’re the temporary owner of all documents saved to their OneDrive for Business.

https://domain-my.sharepoint.com/personal/username_domain_com/_layouts/viewlsts.aspx