Like in this part of the phpmyadmin folder of the config.inc file
$cfg['Servers'][$i]['auth_type'] = 'config'; // Authentication method (config, http or cookie based)?
$cfg['Servers'][$i]['user'] = 'root'; // MySQL user
$cfg['Servers'][$i]['password'] = ''; // MySQL password (only needed
// with 'config' auth_type)
$cfg['Servers'][$i]['only_db'] = ''; // If set to a db-name, only
// this db is displayed in left frame
// It may also be an array of db-names, where sorting order is relevant.
Be careful and make a backup incase of a mini disaster like not being able to use phpMyAdmin at all.