How do I programmatically set the Return Key for a particular UITextField?

For the first UITextField, Read THIS tutorial on how to create a button on a Keyboard. You can learn the logic from there and use a Next button instead of Done button.

   //if you just want to make it appear NEXT//

    textField.returnKeyType = UIReturnKeyNext;

And for the second UITextField, use…

   // for DONE //

    textField.returnKeyType = UIReturnKeyDone;

You can in general create and rename the button to anything, and make sure you give the right IBAction on the event that that button is pressed. In case you do create your own custom button, look at the tutorial above to learn about placing it in the right coordinates and stuff.