Lost database with export error?

I was following instructions to export a database in preparation for ftp transfer. Instead of clicking ‘save as file’ in mamp local host phpadmin – I made the mistake of saving it in the browser window as an html.
I’m surprised it should have done anything to alter the original file, but everything seems to be gone!!
What does/should my database file look like? Where does it reside? [local server..] How can I try and recover it?
Are any of the files housed in the theme folder?

Is the database, the whole collection of files installed from wordpress?
If an import is required, how is that done?

Thanks!