Your question is not entirely clear, but I recommend using Leo's mod(https://itch.io/t/667993/leos-mod) as an example of how to add new items, especially with custom images as icons. The key to that is applying my bugfix patch first, as it fixes many problems related to custom icons. For more detailed help with modding I recommend the Discord (https://itch.io/t/284398/discord), as that is where the most active modders tend to gather.