How to mark zip code as not required in location details

Summary:

We're looking to mark the zip code field under location details for United States country as not required. The ZIP code is set up under "Main Address" region. I tried through Transaction Design studio - Under Actions > Location Details > Page Attributes, however there is no ZIP code field on the list. It needs to be a non required field as we have some remote offices. How can I fix this? Thank you!

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