Siri is giving out wrong phone number for my business
The process used to be opaque and therefore complicated, but Apple now has a self-service web app for small businesses to self-list:


https://mapsconnect.apple.com/


I've not had any issues with updating and creating listings and the email feedback you get is quite helpful if you run into any questions or snags.

If you fail to update your own listing directly with Apple, you can also try to get other data sources like Google Maps, Yelp, etc... correct in case Apple pulls data from other sources. I recommend making an Apple entry for your business rather than letting the system try to guess the correct information.