Many tools are available on the internet to convert OST files to PST, while you search in google. But I strongly suggest the eSoftTools OST to PST Converter Software that quickly migrates OST data to PST including multiple formats vCard, CSV, EML, MSG, PST Outlook, HTML, EML, EMLX and Office 365. The tool can export the desired OST file and provides you the search option through the date range filter option. It keeps the folder structure maintained even after the conversion and migrates the OST file with all it's mailbox components such as emails, journals, tasks, calendars, drafts, and contacts. By using this tool, users can save their OST after conversion to PST at their wished location. This utility has an enhanced and comprehensive user interface, so every non- tech user can use it without any difficulty. Users can use its free demo edition that converts 25 items from per folder.
Get more info: OST to PST file Converter freeware
Get more info: OST to PST file Converter freeware