Add ACF Values in Frontend Form

$new_post = array(
		'post_id'            => 'new_post', // Create a new post
		// PUT IN YOUR OWN FIELD GROUP ID(s)
		'field_groups'       => array(7,58), // Create post field group ID(s) Example is given in below image
		'form'               => true,
		'return'             => '%post_url%', // Redirect to new post url
		'html_before_fields' => '',
		'html_after_fields'  => '',
		'submit_value'       => 'Submit Post',
		'updated_message'    => 'Saved!'
	);
	acf_form( $new_post );

Find your field_groups id from ACF menu –

Now, Submitting the form

add_filter('acf/pre_save_post' , 'save_post_from_frontend' );
function save_post_from_frontend( $post_id ) {

//Check if user loggin or can publish post
if ( ! ( is_user_logged_in() || current_user_can('publish_posts') ) ) {
		return;
}

// check if this is to be a new post
	if( $post_id != 'new_post' ) {
		return $post_id;
	}

        $post = array(
		'post_type'     => 'post', // Your post type ( post, page, custom post type )
		'post_status'   => 'publish', // (publish, draft, private, etc.)
		'post_title'    => wp_strip_all_tags($_POST['acf']['field_54dfc93e35ec4']), // Post Title ACF field key
		'post_content'  => $_POST['acf']['field_54dfc94e35ec5'], // Post Content ACF field key
	);
	// insert the post
	$post_id = wp_insert_post( $post );
	// Save the fields to the post
	do_action( 'acf/save_post' , $post_id );
	return $post_id;

}

Now, Save ACF image field to post Featured Image

add_action( 'acf/save_post', 'save_image_field_to_featured_image', 10 );
function save_image_field_to_featured_image( $post_id ) {

$image = $_POST['acf']['field_54dfcd4278d63'];
	// Bail if image field is empty
	if ( empty($image) ) {
		return;
	}
	// Add the value which is the image ID to the _thumbnail_id meta data for the current post
	add_post_meta( $post_id, '_thumbnail_id', $image );

}