Delegate sharing of Onedrive documents to an administrator

Hello everybody,

I have a little problem an hope someone can help me.

So my users in SharePoint Online have some files and folders in their OneDrive. They share their documents for some other people and everything works fine. But now my problem:
For example, User 1 have a test.txt and share this with User 2, both Users can work with this file.
But now User 1 goes on holidays and the superior of user 1, named User 3, want to access this test.txt.

How can I, the admin, give User 3 access to this txt file? Is it possible and how can I do this?

Thanks for help,

Best regards