Converting an OST file to PST without using Microsoft Outlook can be challenging because OST files are tightly linked to the original Outlook profile and Exchange environment. However, there are still effective ways to complete this task.
One common approach is to use a professional third-party OST to PST converter tools:
DailySoft OST to PST Converter
FixVare OST to PST Converter
SYSessential OST to PST Converter