Autofill an input depending on another input value

Hi everyone, let me explain my issue : - I have a form with 2 select inputs : One for the city and another one for the zipcode. What i want is to autofill the zipcode input depending on the city input value. I tried numerous things and i was only able to filter the zipcode input depending on the city input value but it doesn't autofill it. I've tried to autofill using the "->default()" property but it was not working. Thank you for your help