A lot of solutions are available on the web but first I recommend users to use the manual tricks to convert OST files into PST.

For your help I write 2  articles that will help you to export OST files into PST without any cost using different techniques.

Please follow the below-listed article links that will help you to perfectly convert OST file into PST format.

1: Convert OST to PST Using 3 Different Techniques

2: Convert OST Files into PST Using PowerShell Commands