If you are looking for free ways to convert OLM files into Outlook PST format, I would like to suggest you try the best free manual methods that can easily convert your file format without any interruption. To obtain these free manual methods, read the below-mentioned blog, which contains three manual methods that you can use depending on your version.
To use the methods, you can visit: https://www.datarepairtools.com/blog/methods-to-convert-olm-to-pst-file/