How to add custom fields to a custom Shopify product page using Shopify Line height on impulse theme

[Kahydee]

I am trying to add a custom field to a single product on impulse theme.  I have generated a code using Shopify UI element but I don't know where to paste the code. Each time I paste it on the product-form. liquid on the snippet but it is displaying the custom field for all the products instead of 1 product. I will be glad if anyone can guide me on what to do.

Thank you.