If then logic - corresponding fields

Hello together,

i’m a new user of gravityforms and learning right now about the features from gravityforms.
I build an orderform - it works quit good but i want to give it more useability.

So i want to to the following:
On my form there is a field called PLZ - in englisch = postcode
I’ll only sell to 10 differen PLZ so i would like to bild a drop down field where you can only choose one of the 10 postcodes.
Next to this field there is a textfield where the user have to fill in the City.

Is there a way how this field “city” could be filled automaticly with the corresponding city from the chosen postcode?

I tried to search here in the community but wasn’t shure what would be the keywords i’ve to search for.
If i could get a tutorial / instruction manuel how to build up such a function i would be really grateful.

Nice greetings

Is there only one possible city per postcode?

yes … it would look like this:
58452 -> Witten
58453 -> Witten
58454 -> Witten
58455 -> Witten
58456 -> Witten
58300 -> Wetter
58313 -> Herdecke
58332 -> Schwelm
58339 -> Breckerfeld
58256 -> Ennepetal
45549 -> Sprockhövel

In that case, you could use conditional logic to show one of 10 “city” fields (pre-filled with the default city, and made “read only” if you need to), each one showing only when the postcode selection matches. I can’t think of an easier way to do that.