Populating first address postcode and city with different values

I have a slightly custom user signup process in which the user creates an address on signup using a different method than multiple addresses. Two custom fields have been added to the db during the signup process: email and phone number

When attempting to edit the address using the multiple addresses plugin, the two custom fields don’t appear. I’m not using the postcode and city fields so I’d like to pre-populate the postcode and city fields for the first address with the existing ones in the DB.

How do I remap the values for shipping_city and shipping_postcode to different columns in the db for the first address?

https://www.ads-software.com/plugins/woocommerce-multiple-addresses/