Manual trick
To create a PST file from Office 365, you can use Outlook’s export feature. Go to File > Open & Export > Import/Export, then select Export to a file. Choose Outlook Data File (.pst) and follow the prompts to complete.
Automated solution: I would like to suggest you to take help of Recoveryfix PST to Office 365 tool to easily Import unlimited healthy PST & OST files to Office 365. Get more information, visit to: https://www.recoveryfix.com/import-pst-to-office-365/