Use DRS Convert OST to PST software to convert OST files into different file formats and email clients. The tool is very easy to use and does not require any other special knowledge. You can download its free demo version and check its performance.
See these answer:
https://www.linkedin.com/pulse/4-quick-ways-convert-ost-pst-free-arysontechnologies/?trk=organization-update-content_share-article
https://community.spiceworks.com/how_to/164251-how-to-change-ost-to-pst-in-outlook-2016-2019-2013-manually