Adding additional code to a built iOS app. [modify current API/JSON]

Hello, I have an app which basically acts like Instagram where users are able to upload and view a photos from a MySQL database through JSON. Before a user can view the photo stream and upload their own photos to the database they are required to either login to an existing account or register a new one. However, before the user is prompt to login/register I would like the user to be prompt to enter a "wedding id" name. I want this "wedding id" to essentially select a table within the database with the table having the same name as the wedding id, so once the user logs into the database, the photos they are viewing are from their assigned wedding id. The storyboard and controllers are already laid out, and all that I need now is the coding to make this happen. I can explain more in detail if needed. Thanks, Mike