Please add yourself to every group and add following code in your theme’s (child theme’s if you are using) functions.php

add_filter( 'fep_get_option', function( $value, $option ){
    if( 'can-send-to-group' == $option ){
        if( fep_is_user_admin() ){
            $value = true;
        } else {
            $value = false;
        }
    }
    return $value;
}, 10, 2 );

Then you will see an option to send message to group when sending message.