To convert an OST file to PST using the VSPL OST File Converter tool, follow these steps:

1. Download and Install: Get the VSPL OST File Converter tool from its official website and install it on your computer.
2. Launch the Tool: Open the application after installation.
3. Add OST File: Click on the Add OST File button and browse to select your OST file.
4. Choose Output Format: Select PST as the output format.
5. Set Destination: Choose a location where you want to save the converted PST file.
6. Start Conversion: Click Convert to begin the process.
7. Complete: Once done, access your PST file from the designated location.

More info- https://www.vartikasoftware.com/product/vs-ost-to-pst-converter-software.html