I noticed, after trying it myself, in the video after the challenge the instructor copies the end keyframe of Swing_Down to use as the start point for Swing_Up. Alternatively I found if you copy all the keyframes, then open up Swing_Up, move the preview to whatever key the Swing_Down finished at hit paste and then Drag the ending frame to the 0 frame Unity will basically reverse the animation for you. I was worried about getting my animation to not look all shakey if I messed up some intermittent keyframes but it seemed to work really well this way. 
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Copy Paste all Keyframes from Swing Down, then select all keyframs and use the handles to scale and flip the sequence of keyframes.