Custom Table for Taxonomy with WPGridbuilder

Hi!
I'm using WPGridbuilder to query the terms of a custom taxonomy.

I have a Single Image field and want to use it as feature image for terms.

WPGridbuilder provided this code to show the Single Image field:

function set_custom_card_thumbnail( $object ) {

	// Get settings of the current grid.
	$grid = wpgb_get_grid_settings();

	// If it does not match the grid ID 1.
	if ( 1 !== $grid->id ) {
		return $object;
	}

	// You have to change "custom_field_name" by yours.
	$image_id = get_term_meta( $object->ID, 'custom_field_name', true );

	if ( ! empty( $image_id ) ) {
		$object->post_thumbnail = $image_id;
	}

	return $object;

}
add_filter( 'wp_grid_builder/grid/the_object', 'set_custom_card_thumbnail' );

The code works perfect for a single image field with data is stored in post_meta.

But I don't know how to use it when I store the single image field data on a custom table.

Please help! Thanks