You can try vMail OLM to PST Converter to perform a secure migration from OLM to PST format in a matter of seconds. The program export OLM to PST in a secure way, including all mail attributes, emails, and attachments. It works with OLM files from all Outlook versions and may convert a single or more OLM mailbox at once. You can download the free demo version and export few emails from each mailbox folder.
Know more info- https://www.vsoftware.org/olm-to-pst-converter.html