If you want to save your time you can directly take the help of MailsDaddy PST to Office 365 Migration Tool. Using this solution users can effortlessly migrate PST to Office 365. Here users can directly upload PST files into Office 365 Primary and In-Place Archie mailboxes.
Know more: https://www.mailsdaddy.com/pst....-to-office-365-migra

If you are still searching for OST to PST converting tool for migrating the OST file into PST file format, then you can go with the MailsDaddy OST to PST Converter tool. Because
1. It provides multiple file migration at once.
2:- Export OST to PST, EML, MSG, MBOX, contact in CSV and calendar in ICS format
3. Conversion result does not vary from the actual.
4:- Helps to view the preview of overall PST file databases.
5. Migration can be also done into Live Exchange Server and Office 365.
6. It converts all data fully not partially.
7:- Can be installed on overall Windows systems.

Visit here: https://www.mailsdaddy.com/ost-to-pst-converter/