Using a free OLM to PST conversion tool is not recommended as it can be unreliable and may not provide the same level of quality as paid software. Additionally, the conversion process may be more difficult, and you may get a different level of support than paid software.

We always suggest using any third-party OLM to PST converter. In this case, you can try out the Regain OLM converter. It's quite good and budget-friendly.

If you still want to try a free method, alternatively, you can follow these steps:

Open Microsoft Outlook and go to the "File" menu. Select "Import and Export" and then choose "Export to a file." Select "Comma Separated Values" as the file type to export to, and choose the folder that contains the OLM file. Choose the exported file's destination folder and filename, and then click "Finish." Once the export is complete, open the exported file in Microsoft Excel or another program that can open CSV files. Save the file as a PST file by selecting "File" -> "Save As" and choosing "Outlook PST" as the file type.

Note: This method may not convert all the elements of your OLM file, such as attachments, and may not work for large OLM files. Additionally, it may require manual labor and is not guaranteed success.

Read more: https://www.regainsoftware.com/olm-to-pst-converter.html