Do you mean variation options, where a buyer can select from different colours in a dropdown menu?
If so, once a listing has been submitted, the format can't be changed and unfortunately you can't add variations if the variation format wasn't used to list the item, which would mean having to end the listing and create a new one using the variation format.
If the listing did use the variation format, you will have to revise the listing and click the Add/Edit variations link (third section down).
