minecraft-assets/data/minecraft/recipe/netherite_helmet_smithing.json

{
  "type": "minecraft:smithing_transform",
  "addition": {
    "item": "minecraft:netherite_ingot"
  },
  "base": {
    "item": "minecraft:diamond_helmet"
  },
  "result": {
    "count": 1,
    "id": "minecraft:netherite_helmet"
  },
  "template": {
    "item": "minecraft:netherite_upgrade_smithing_template"
  }
}