Modify code to create gallery

Hi help please
What should I change or add in the code so that the image or video of the nft remains as a featured image automatically, in order to create a gallery of multiple collections
Thank you.

`// Create NFTs CPT
public function initialize() {

$labels = array(
‘name’ => _x( ‘NFT’, ‘post type general name’, ‘wp-smart-contracts’ ),
‘singular_name’ => _x( ‘NFT’, ‘post type singular name’, ‘wp-smart-contracts’ ),
‘menu_name’ => _x( ‘NFT’, ‘admin menu’, ‘wp-smart-contracts’ ),
‘name_admin_bar’ => _x( ‘NFT’, ‘add new on admin bar’, ‘wp-smart-contracts’ ),
‘add_new’ => _x( ‘Add New NFT’, ‘NFT’, ‘wp-smart-contracts’ ),
‘add_new_item’ => __( ‘Add New NFT’, ‘wp-smart-contracts’ ),
‘new_item’ => __( ‘New NFT’, ‘wp-smart-contracts’ ),
‘edit_item’ => __( ‘Edit NFT’, ‘wp-smart-contracts’ ),
‘view_item’ => __( ‘View NFT’, ‘wp-smart-contracts’ ),
‘all_items’ => __( ‘All NFT’, ‘wp-smart-contracts’ ),
‘search_items’ => __( ‘Search NFT’, ‘wp-smart-contracts’ ),
‘parent_item_colon’ => __( ‘Parent NFT:’, ‘wp-smart-contracts’ ),
‘not_found’ => __( ‘No NFT found.’, ‘wp-smart-contracts’ ),
‘not_found_in_trash’ => __( ‘No NFT found in Trash.’, ‘wp-smart-contracts’ )
);

$args = array(
‘labels’ => $labels,
‘description’ => __( ‘Description.’, ‘wp-smart-contracts’ ),
‘public’ => true,
‘publicly_queryable’ => true,
‘show_ui’ => true, // this removes UI from wp-admin
‘show_in_menu’ => true,
‘menu_icon’ => plugin_dir_url( dirname( __FILE__ ) ) . ‘assets/img/icon-nft.png’,
‘query_var’ => true,
‘rewrite’ => array( ‘slug’ => ‘nft’ ),
‘capability_type’ => ‘page’,
‘has_archive’ => true,
‘hierarchical’ => false,
‘menu_position’ => null,
‘supports’ => array( ‘title’, ‘editor’, ‘thumbnail’ )
);