You must use third-party applications if you want to convert big number of OLM files, and consumers claim that vMail
OLM to PST Converter is the finest option because of its special characteristics, which make it
efficient and 100% confident in its abilities. The output data can also be
saved in a variety of formats, including PST, EML, MBOX, EMLX, vCard,
vCalendar, MSG, and HTML. It offers a preview option that allows you to see a
sample of the recovered mailbox prior to conversion and produces results that
are satisfactory and meet your needs. With this, you can effortlessly and
without any problems extract data from an Outlook OLM file into a PST file
format.
Know more info- https://www.vsoftware.org/olm-to-pst-converter.html