The OST is just a cached version of the mailbox on the mail server. Where was the mail server? Can you reconnect to it?
This is your personal Outlook? Not Outlook connected to an Exchange server?
I can't say that I've ever tried this. This tool seems to have a free version that lets you preview the results and see if you are happy with it at least. Maybe you could give that a go. I would suggest making a copy and backing up that OST file first. If you are wary of malware, try it on a different computer you don't care about and get your emails back, make a PST and import it into your primary machine.
https://www.stellarinfo.com/convert-ost-to-pst.php