Summarize:

Cover all of the gum's surface area, if possible. Be careful not to tape the entire strip of duct tape to the garment or fabric or getting it off will be doubly difficult. Remove gum from duct tape manually or cut off a new strip to repeat.
Cut a strip of duct tape off its roll. Take the duct tape and press it firmly on the gum. Peel off taped area. Repeat until all the gum is removed.