To access different OneDrive accounts you must be a secondary administrator for each of the Site Collections that represents the accounts.

Here is the manual procedure - Link to a nice BLOG that visually describes the steps.

For the automated procedure instead you can write a custom Microsoft SharePoint online script (which is indeed a power shell script) to set an user as secondary administrator.
Use the below powershell script to do this. save the below snippet to file.ps1 and run in sharepoint online management shell.

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