OST to PST Converter
To convert ost files into pst files, download the Microsoft ost-to-pst converter software. All ost files can be converted to pst format using the Stella Microsoft ost-to-pst software. Stella Microsoft ost-to-pst converter software converts all ost items into an office 365 account. Stella Microsoft ost-to-pst converter software converts corrupted data from ost files to pst files.
For more information, please visit this link. https://www.stelladatarecovery.com/email-migration/ost-to-office-365.php
lewis hamilton commented
Launch the MS Outlook program on your system.
Go to the File tab.
Select the Import/Export option.
Click on Export to a file.
Hit the Next button.
Now select Personal file folder (.pst)
Click on the Next button.
Go to parent root and click on Include Subfolders.