Can you import an ost file into Outlook? then I have a smart solution that can convert OST file to PST with all items of OST Mailbox. Check out the software from eSoftTools as OST to PST Converter software.
Superlative solution - https://www.esofttools.com/ost-to-pst-converter.html
Superlative solution - https://www.esofttools.com/ost-to-pst-converter.html