How to add a new field to a form Rails?

I am trying to add a new filed to a form with Rails for each field needs to have a dropdown of shipping options with the value of: shipping_option_id:

How do I do it with form?

Schema

 create_table "products", force: :cascade do |t|
    t.string "sku"
    t.string "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.bigint "shipping_option_id"
    t.bigint "product_region_id"
    t.index ["product_region_id"], name: "index_products_on_product_region_id"
    t.index ["shipping_option_id"], name: "index_products_on_shipping_option_id"
    t.index ["sku"], name: "index_products_on_sku", unique: true
  end