inbox_args.php

<?php
add_filter('gravityflow_inbox_args', 'registrations_inbox_form_ids', 10, 1);

function registrations_inbox_form_ids( $args ) {

	//Specify which instance of the shortcode you want to affect
	if( false !== strpos($args['detail_base_url'], '/event-registrations/') ) {
	
		$registrations = array( '106, '107');
		
		//Or derive from a looop of all forms with a specific setting enabled
      		/* 
		$forms = GFAPI::get_forms();
		$registrations = array();
		foreach($forms as $form){
			if( isset( $form['enable_registration'] ) && $form['enable_registration'] ) {
        			$registrations[] = $form['id'];	
			}
    		}
		*/
	$args['form_id'] = $registrations;
    	$args['fields'] = array();
    	$args['fields'][] = "2";

  }

  return $args;
}
?>