I would commend OST to PST Converter software, which allows to the recovery of data from corrupt MS Outlook OST files and Convert OST file to new PST files. By using its app you can quickly transfer OST file to PST file and save all MS Outlook OST files many items like email, task, draft, notes, attachment, contact, and inbox, calendar (To, Cc, From, Date, Time, Subject, Object and Bcc). The app will resolve all problems with MS Outlook OST file and, as a result, convert them to PST and a variety of other file formats, including- PST file, Office 365 files , Zimbra, Gmail, EML, EMLX, vCard, ICS, MSG, Live Exchange server, MBOX and etc...

Convert OST to PST Manually

https://www.kdetools.com/blog/how-to-convert-ost-to-pst-manually.html