首先是例子，然后是解释。
执行更改的方法：

const setSkuDescription = (
    value: string,
    index: number,
    field: FieldArrayWithId<Fields, 'product', 'id'>
): void => {
    update(index, {
        ...field, // all the info in the current object field this is required and not partial (they say is in the doc)
        productID: value, // one of the fields i want to update
        skuDescriptions: rawProducts // another field i want to update
            .map((p) => {
                if (p.ta_name === value) return p;
            })
            .filter((p) => p !== undefined) as Product[]
    });
};

其中im使用该方法：

<CFormSelect
// this is for reference to you to see where to use the method
  onChange={(d) => setSkuDescription(d.currentTarget.value, index, field)
}>
    <option hidden>---</option>
    {products.map((product, key) => (
        <option value={product.value as string} key={key}>
           {product.label}
        </option>
     ))}
</CFormSelect>

反映变化的地方

<CFormSelect
{...register("product.${index}.description", { // this is for reference to you to see where the method will render in the HTML if you need it
     required: "The field SKU Description is required"
 })}>
     <option hidden>---</option>
     {field.skuDescriptions.map((p, key) => (
         <option value={p.ta_productid as string} key={key}>
            {p.ta_size}
         </option>
      ))}
</CFormSelect>

解释：首先是接收3个参数的方法。第一个是你想要修改的“值”，第二个是数组在Map时给你的数组索引，最后是整个field对象返回数组的Map，因为这需要用来更新对象的所有信息（这部分参考官方文档）。
required information in the docs