When you use candy melts like Wilton's... do you have to add corn syrup to it to make it modeling chocolate?

You melt them and add your corn syrup and then stir it in, cool it and go for it right?

the recipe is usually on the back of the bag but you are correct that you add corn syrup. I just don't know the amounts

Here is a recipe posted: You can search candy clay and get a better printed version too!
Candy Clay for Modeling & 3D Figures

Ingredients

14 oz. Package of Candy / Chocolate Melts
1/3 cup light corn syrup
Instructions

Melt Candy Melts following package directions. Add corn syrup and stir to blend. Turn out mixture onto waxed paper and let set at room temperature to dry. Wrap well and store at room temperature until needed. Candy Clay handles best if hardened overnight.
To Tint: Candy Clay may be tinted using Wilton Candy or Icing Color. Knead in color until well blended.
To Use: Candy Clay will be very hard at the start; knead a small portion at a time until workable. If Candy Clay gets too soft, set aside at room temperature or refrigerate briefly. When rolling out Candy Clay, sprinkle work surface with cornstarch to prevent sticking; roll to approximately 1/8 in. thickness.
To Store: Prepared Candy Clay will last for several weeks at room temperature in a well-sealed container.