Do note that standalone users are not required for normal use - when MySQL databases are created, a user will full permissions is created with them.
Assuming that you have already created the MySQL database and the standalone user, you then need to login as the original database user (ie, click the 'Now' button under 'Manage' for the databse) and then run the following SQL command:
GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, LOCK TABLES ON `webXX-dbname`.* TO 'n-webXX-user'@'%' WITH GRANT OPTION;
Replacing webXX-dbname with the original database name, and n-webXX-user with the standalone username.
If there are any other privileges that you need granted on a database, that you don't have access to, please get in touch with our support team with your request.