Creating Custom Merge Tag, like magic_tag from Caldera Forms

Hi dear support/community, i wanted to know if there is a way to transfer custom merge tags from caldera forms (since it is no longer a supported plugin) to ninja forms or how to create custom merge tags that get values from the database like in this code example. i basically want to populate a form with an event id with prepopulated data based on the url with an event_id.

add_filter( 'caldera_forms_do_magic_tag', function( $value, $magic_tag ) {
    if ( $magic_tag == '{my_event_id}' ) {      
      if (empty($_GET['event_id'])) {
        return '';
      }

      return $_GET['event_id'];
    }

    if ( $magic_tag == '{my_workshop_name}' ) {
    	if (empty($_GET['event_id'])) {
        return '';
      }

      global $wpdb;

      $amelia_workshop = $wpdb->get_results(
        "SELECT events.name
        FROM wp_amelia_events events
        JOIN wp_amelia_events_periods periods
        ON events.id = periods.eventId
        WHERE events.id = " . $_GET['event_id'],
        OBJECT
      )[0];

      return $amelia_workshop->name;
    }

    if ( $magic_tag == '{my_event_date}' ) {
      if (empty($_GET['event_id'])) {
        return '';
      }

    	global $wpdb;

    	$amelia_workshop = $wpdb->get_results(
	      "SELECT periods.periodStart
	      FROM wp_amelia_events events
	      JOIN wp_amelia_events_periods periods
	      ON events.id = periods.eventId
	      WHERE events.id = " . $_GET['event_id'],
	      OBJECT
	    )[0];

	    $event_date = $amelia_workshop->periodStart;

	    return date_i18n( get_option( 'date_format' ), strtotime( $event_date ) );
    }    
 
    return $value;    
}, 10, 2 );