The bigdump script has over 1000 lines, so I suspect your copy is corrupt. You might want to download a fresh copy of the ZIP archive and extract the bigdump.php file again. URL:
https://www.ozerov.de/bigdump/
Also note that you probably can’t import the .sql files until you create a database. Most SQL dumps do not attempt to create databases because control panels such as cPanel/Plesk/DirectAdmin/etc set up DB users that do not have the ability to create databases.