Autopopulate field based on answer of previous field

I'm trying to set up a form where Dropdown1 is a list of police departments to choose from.  I would like it to autopoluate the address of the department chosen into the next texbox of the form.  I have created an export value (address) for each police department in Dropdown1.  Where I run into issues is setting up the next field to accept the export value of the previous field.  I have tried various scripts found in other posts but none seem to be working.  I think I'm either missing a step or the others are not requesting exactly what I am looking for.  I am a novice at scripts.  Thanks!