Add the sample code below to your child theme's functions.php file or in a site specific plugin. Then change the text after the arrow to something of your choice.

<?php
//* Do NOT include the opening php tag

//* Change MailChimp to retrieve up to 50 lists
function tw_limit_mailchimp_list_call( $params, $mailchimp_controler ) {
    $params['limit'] = 50;
    return $params;

}
add_filter( 'FHEE__EE_MCI_Controller__mci_get_users_lists__list_params', 'tw_limit_mailchimp_list_call', 10, 2 );