Is there anyone that might be able to help me with support here? Please see message body

I have posted this here already, but also on the mozilla website, and am unable to get it resolved. I need to try to convert a PST to MBox without Outlook (Or one that is no longer actively able to be downloading e-mails), and I do not understand how to import a CSV file for the address format due to not a lot of information regarding comma formatting, and the fact that these things become excel spreadsheets, and all I have that is more current is Libre Calc. My primary provider for email was So if somebody can help me, it would be appreciated greatly.