In my experience, I suggest Mailsdaddy OST to PST converter. This tool is 100% safe and reliable to convert OST to PST format in few clicks. You can also export multiple OST into PST format as well as you can save it on the spot into the given formats. The device has already been tested in large data files, so there is no file size limit and you can split your OST file into several PST formats.
Here, you can explore the all steps: https://www.mailsdaddy.com/ost-to-pst-converter/