When choosing edit mode from the Choose A Mode menu, you will be taken to a new screen that is different from the study and test modes. There is no button to show stats or a timer, but Card n of x is still displayed at the top with x denoting the total amount of cards in the collection and n denoting which card you're currently viewing.
You'll notice that in the main box, the question is displayed and then there is a text area directly underneath it, and directly below that is the same setup for the answer to the card. If you begin typing in the question text area, it will change in real time and display what you're writing in the question above the text area. The same is true for writing the answer. This can be very helpful to fix typos or correct an answer if it's incorrect.
Below the question and answer section, you will notice 3 buttons at the bottom, Add Card, Remove Card and Confirm. If you are currently viewing card 1 of 5 and you click the add card button, it will take you directly to card 6 of 6 and contain an empty question and answer. You can then begin to write out the question and answer and again it will display in real time. Once you're satisfied with the new card, in order to successfully add it to the collection you MUST click the confirm button. The confirm button is the only button that will cause any saving to happen. So if you are on card 3 of 6 now and you decide that you want to remove it, you can click the remove card button which will remove it from the collection in real time as you're viewing it, however, you MUST click the confirm button to save the changes. This is used as a safeguard in case you accidentally remove the wrong card.
Finally, like all of the other modes there is a Main Menu button at the bottom of the page and clicking it will take you directly back to the main menu.