If you use manual process to convert OLM data into PST format is little bit risky. Manual method is very lengthy process which take lots of time to process and technical person can enable to run this process. I called it risky because if you are not aware during manual process then it can lead huge loss of original data so if you don't wanna to lose your original data then you shouldn't dare to use manual process. then question is how to convert olm data into pst without any loss then i suggest you to use any third party software which is know as reliable method to secure your original data during conversion. If you want any recommendation then i would like to recommend you to use this OLM to PST converter software which can export single or multiple OLM data into PST format in just single way.
It allows the User Export the OLM file to PST and Multiple file types such as HTML, MBOX, EML, PDF, vCard, EMLX, MSG, and vCal file type. This tool Export all the OLM file, Emails, Attachments, Journal, Notes, Contact, Calendars, and etc. to PST format. The OLM to PST converter can Export OLm files to Office 365 and a Live Exchange server Safely then Export the OLM Contacts and Calendar to vCard and vCal files.