If you want to import an OST file to Outlook, you can try some techniques such as, Import/Export Wizard, drag and drop or use of other tools. Traditional approaches such as file sharing through email, sharing of folders on computer networks, and physical transfer through means like flash drive are slow and cumbersome. But for the best and efficient manner, it is recommended to go with Shoviv OST to PST Converter.
Read more- https://worldnewsfox.com/technology/how-to-import-ost-file-to-outlook-using-best-ost-to-pst-converter/
CubexSoft OST to PST Converter Tool is the perfect offline solution. You can simply install and run this tool on any Windows OS and Mac to export Offline Outlook OST files to PST, PDF, MBOX, EML, MSG, CSV, etc. It works even without an internet connection so it is much safer than an online OST Converter.