Calendar data can also be separated from OST files by going through two methods of your own: First, utilize Outlook's Import/Export feature: By opening outlook, go to File – Open & Export – Import/Export and import the calendar for export to a PST file. Second, the exporting can always be done to ICS format, and selecting the desired option will save the calendar as an ICS file. The more efficient tool is the WebbyAcad OST Converter Tool: this program is capable of extracting calendar data even while the OST files cannot be accessed.
For more information:- https://www.webbyacad.net/blog/best-methods-for-calendar-extraction-from-outlook-ost-files/
