I know you can add a draft angle to a body when extruding it by simply moving the “draft arrows” located above the extrusion arrows. However, I couldn’t find a way to add a draft for a part that has already been extruded before. That is, once you confirm extrusion height, you can no longer add a draft to that part.
Select the border of the face you set the draft angle on and select the scale tool. If you are intending to get it to a specific angle you will need to draw a separate line at that angle and match it since this way only gives you a percentage adjustment.