Once a incorrect station id is assigned I don't think it can be changed except with some WU help which if it can be done will likely take a while.
I would suggest it's better to register a new one, you can have multiple station ids as I do per my forum sig. You will lose your current stations history so if you don't want that you might opt to wait for WU help.
Otherwise, register again and just make double sure you have correct station lat long, elevation and city/zipcode.
Then just bookmark the new WU station page and go forward, the old one will fall off the map eventually when you change to the new one and it's data source dries up.
I will tell you I registered with 85379 and WU's iOS mobile app displayed all three station as Sun City AZ but I live in Surprise AZ. The USPS has those two cities both associated with 85379 and although my station ids were correctly created as KAZSURPRxx WU incorrectly displayed Sun City instead of the USPS suggested primary city of Surprise. Eventually I figured that out if you tap on the city/state name displayed you can change it to a "Nickname" i.e. "Surprise, AZ" in my case.
I complained about it and eventually they replied that they are supposedly fixing it in a future release.