Theme_My_Login::register_form()

public function register_form( Theme_My_Login_Form $form ) {

    $this->forms[ $form->get_name() ] = $form;

    /**
     * Fires after registering a form.
     *
     * @since 7.0
     *
     * @param string              $name The form name.
     * @param Theme_My_Login_Form $form The form object.
     */
    do_action( 'tml_registered_form', $form->get_name(), $form );

    return $form;
}

View src/includes/class-theme-my-login.php, line 147 on GitHub