MacSonik OST to PST Converter for Mac is an excellent utility of software for converting OST files to PST format with complete accuracy. This OST to PST converter is a popular tool for Mac users who want to convert OST files to PST files on a Mac device that contain emails, contacts, calendars, tasks, notes, and all mailbox items. This program converts OST data files to EML, MBOX, PDF, DOC, DOCX, CSV, and other file formats. Users can also import OST emails into Gmail, Yahoo, Thunderbird, Office 365, IMAP, iCloud, and other fantastic services

You can convert OST to PST with CloudMigration OST to PST Converter Tool.  This tool converts OST to PST, PDF, EML, EMLX, etc.  You can easily migrate OST to Gmail, AOL, Thunderbird, etc. It has a simple and interactive GUI. It supports all windows versions. You can try this tool with its free demo version.

There are many tools available to convert ost to pst like stellar, systools  and you can also manually try to convert them but it would take a bit of help. Is there a reason why you  want to convert them