Responses are listed in the response list, which can be accessed by swiping your screen to the right from the form list or by clicking on the responses tab above (in Android).
Once you are there you can see that all the listed responses contain a blue info icon.
By clicking this icon you are accessing properties of the response and functions that you can perform on this response.
This will delete this response from the mobile device. For responses that are not sent yet this function will stop them being uploaded also.
This will get you back to your response. If not sent, the response is open to modification. Otherwise the form fields will be greyed out and available only for review.