To export a PST file from Office 365, you can use the MS 365 admin center or the Exchange admin center. Here’s a general outline of the process:
 
●       Sign in to the Microsoft 365 admin center or the Exchange admin center.
●       Go to the user’s mailbox that you want to export, and then select the Export option.
●       Follow the prompts to choose the items you wish to export and specify where to save the PST file.
●       When the export process is complete, it will automatically save the PST file to the specified location.
Additionally, you will need any professional Regain PST to Office 365 Migration Tool software to do the process automatically. Non-technicals use it to avoid additional data losses