Hello
you will need to modify the phpmyadmin config file
it has examples in it You can also install a new
copy of the regular phpmyadmin in your customer's /user's directory and configure it for them this is the best way it keeps them from having too much access to your server the config file can be set to give them access to just their database just un-zip the phpmyadmin into their directory change the config file and on your server use your phpmyadmin to add that user with the permissions you want to give them
they can use their copy to add or make changes they want to their database