RRyan1-
As far as I know, the Zipcode you enter into the Roku TV is used for getting the channel guide information for local channels you receive over the air via an antenna hooked up to the antenna port on the set.
If you are not using an over-the-air antenna, you are receiving your locals either from Starlink as a cable TV service or from some streaming service.
If you use Starlink as a cable TV service, they should deliver the correct set of locals according to your home address. If not, contact them.
If using a streaming service for your locals, check your settings for any such app for a way to set your location. You may need to do this on their website.
If they don't give you an option for setting hour location, they probably rely on the location associated with your assigned IP, which you already know does not represent your actual location. Your only recourse at that point is to contact Starlink and tell them you need for them to assign an IP to you that reflects where you live.