You would FTP in to download, view and modify your .htaccess file and then upload it after you make the desired modification. More info here. For FTP, I use Filezilla.
You would have had to do this previously to modify the .htaccess file with any additional rules. If you did not, was this a migrated site? If so and depending on how that process was accomplished, then that file could have moved with everything else.
Judith "I failed my way to success." ~Thomas Edison