tml_admin_extension_update_message()

function tml_admin_extension_update_message( $data, $response ) {
    if ( empty( $response->package ) ) {
        echo ' ' . sprintf(
            '<em>In order to enable automatic updates, please enter and activate your <a href="%1$s">license key</a>.',
            esc_url( admin_url( 'admin.php?page=theme-my-login-licenses' ) )
        );
    }
}

View src/admin/extensions.php, line 307 on GitHub