For example, in the screen shot below you can see that a name format field already exists:
User-added image
  1. In Selected fields (right-most column) click on the root field, such as Constituents in above screenshot, to highlight the field.
  2. From the middle column, bring over Name Format into Selected fields once more which will create a second row for Name Formats.

Click here to review a video covering more about the export process and export definitions. You can also review written information on export definitions and the export process.