We automatically pull all information about venues (name, location, categories) from Foursquare. If you are noticing an error in this information on Untappd, it will first need to be changed in Foursquare.
Note that you will need to have a Foursquare/Swarm account and be signed into it. Find the venue on Foursquare and select "Suggest an edit."
It may take multiple edit requests to update information. If you notice the information hasn't updated after you have suggested an edit, you can reach out to Foursquare Support. It does take up to 24 hours for an edit made on Foursquare to reflect on the Untappd page.