Touch and hold on a watch face. Choose Edit.
Go to the Complications part and select a current complication to change. Or add a complication if you have room for an additional one.
If you select a current complication, you then need to touch the < (top left of the screen). Choose Contacts, and you should see My Card at the top.
If you are adding one to a free space/empty space for a Complication. Touch and hold, choose edit. Then scroll down to Contacts, and again you should see My Card at the top.