Unfortunately, there is no free OST to PST Converter but yes tool like EmailsGuru OST to PST Converter available free trial version for users. It is specifically designed to convert OST file to PST format. This tool This preserves all email data, including attachments and folder structures during the conversion process. It is developed with an advanced and modern algorithm, which makes it safe and best way to convert OST file to PST. Moreover, this tool seamlessly works on all versions of Windows Operating Systems.

For a free demo: https://www.emailsguru.com/ost/pst/