Open an option set, click the field in the preview and open Show when.
Pick When a field above has a value to follow another field, for example a gift message that shows once the shopper ticks “This is a gift”.
Or pick When a product option is selected to follow a product option, like a size.
Go back to the field list and try it in the preview: the field appears when its rule is met.
Under Products, choose where it shows, then click Save.
Still stuck?
Open the app in your Shopify admin, go to Help and click Chat with us, or email [email protected] with your store’s myshopify.com address.