This article is what you should do after you have downloaded the Crisp app, if you haven't downloaded the Crisp app yet, please refer to this article:

Setting Up a New iPad

  1. You will first need to open the Apple Settings app.
  1. Once you've opened the app click on the WiFi button and make sure you're connected to the Crisp Wifi (CRISP-[STOREID]) - each WiFi is different according to your store ID

Once connected, you can quit out of settings and go into the Crisp App. Once in the  Crisp app, log in with your Pin code, and open the side navigation by hitting the icon with 3 lines in top left of the screen. Or swipe out from the left side of the screen.

Go to the bottom of the list to Settings
From here you can select the receipt printer, payment device, and register you want to associate your device with. 

View instructions here:

Note that the Register setting will determine where any cash payments will be expected when doing a cash drop.