Cannot run the script provided by config tool

Hi,
Im using plesk with phpMyAdmin.

First thing I would like to understand, Do I need to create new clean DB to use the plugin?
Or should I use my Exciting DB?
The one I've opened to my WP multisite on first installation, I already have some plugin tables on it.

Second, I've started the progress using my exciting DB and paste the code I got from the tool (https://premium.wpmudev.org/db-tools/db_sql.php) to my SQL Tab on phpMyAdmin and got the meesege (After click on GO):
Error
SQL query:
CREATE DATABASE MYDBNAME_00 DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;

MySQL said: Documentation
#1044 - Access denied for user 'MYDBUSERNAME'@'%' to database 'MYDBNAME_00'

Thanks