The sill cap is along the top edge of the sill. Depending on the type of this, this could be a composite material, wood material or plastic. Some sill caps can be removed and replaced due to normal wear.
In this video, Therma-Tru provides a comprehensive, step-by-step, tutorial explaining how to replace an adjustable sill cap in a door unit. Replacing an adjustable sill cap requires using tools that are not provided by Therma-Tru. Feel free to contact Therma-Tru with any questions or concerns about maintaining a door unit.