Custom fields on product page

I’m having trouble with
Pre populating custom text fields in product page

Working in
WIX standard store, Velo

Site link
If this is happening on a site, include a live or test site link

What I’m trying to do
I have a standard WIX store with products. Products have a custom text field ‘Order Code’. I want to pre-populate the ‘Order Code’ on the product page when the user reaches it, with a value stored in local storage.

What I’ve tried so far
Tried using velo to assign the value to the custom text field, but it does not seem to be exposed to inject any value into that field (other than if its typed in by the user)

Extra context
Anything else that might help - edge cases, screenshots, etc.