Click the Names & Numbers Button on the bottom of the screen

Select On/Off for Names, Numbers, Choose the side of the garment you want your names/#s on, the size and then select Enter Custom List

Enter your sizes / names and #s and save and close

Once you've entered your names and numbers, the design studio will show "NAME" and "00" as placeholders, since the actual information will differ from shirt to shirt, based on the list you've provided.