Simply create a new database from scratch and give full access to that user on the newly created database.
Create the database
$ mysql -u root -p $ mysql > create database example_com;
Granting database access to user
grant all privileges on database.* to database_user@localhost identified by 'password'; flush privileges;
with the example stated above it could be something like this
grant all privileges on example_com.* to example_user@localhost identified by 'secret'; flush privileges;