add_filter( 'woocommerce_simple_auctions_placed_bid_message' , 'custom_woocommerce_simple_auctions_placed_bid_message', 10, 2);

function custom_woocommerce_simple_auctions_placed_bid_message ($message,$product_id ){

	$product = wc_get_product($product_id);
	$current_user = wp_get_current_user();

	if($current_user->ID == $product->get_auction_current_bider()){
		if(!$product->is_reserve_met()){
			if('yes' === $product->get_auction_sealed() )
				$message = sprintf( esc_html__( 'Successfully placed bid for "%s"!', 'wc_simple_auctions' ),$product -> get_title()  );
		} 
	}

	return $message;

}