Last week, I created 7 checkbox fields with values Checked and Unchecked, and added them to a screen. Today, I edited the screen and viewed the checkboxes for the first time, and was not satisfied with their appearance/function. I decided to instead create one checkbox, with 7 options. However, when I tried to add the new field to my screen, I couldn't find it. I had associated the new field with my screen. What step did I miss?