Where and how do I get to the local folder?

Help!

However I can’t get past finding the local folder to then import the mbox file?

Nobody knows the name of the folder where you stored those messages. Can you post a screen shot of this "local folder" and its contents?

Import, at least using some versions of import, put messages into a local folder. But some do not. If it did and you have a different folder associated with your EMAIL, just select and move messages into the folder of your choice. Last time I had to do such imports it had put messages into subfolders of "Local Folders". In my most recent use was dealing with conversion earlier this year, I was convering a client from POP to Imap from PST (outlook) messages which was a bit messy as wanted all but fairly recent messages only on Local folders with messages going back 15 years. So most messages needed to be archieved to avoid attempts to sync back to IMAP folders on server. Also used the Remove Duplicates option.

If just using IMAP then you don't need to import as messages will sync from server.

“Local folders” is an account in Thunderbird for storing messages only on your computer. You will see it in the folder pane that shows all your accounts.