The best method for converting OST files to PST format, Use the third-party tool. It helps to easily convert the data but if the tool is perfect and reliable. I would suggest the best and reliable tool,
Shoviv OST to PST converter.
The OST to PST converter tool converts the multiple OST data to Outlook PST formats and it also recovers the corrupted and inaccessible OST data items such as email, contact, task, calendar, Journal, etc. It also exports OST data into Office 365, Live Exchange Server, EML, MSG, and HTML Formats.
Some Important highlights of Shoviv OST to PST converter
-Quick and provides the error-free conversion from the converter
-Recover deleted and inaccessible OST data
-Converts multiple OST data into Outlook PST, Live Exchange Server, Office 365
-Save data into EML, MSG, and HTML formats
-Supports all versions of Outlook, and Windows OS
-Download its demo version and check the ability and convert the first 50 items per folder
More details, visit:-
Convert OST to PST free