1. Put a leg on the deck with boot toe placed over folding activation lever arm
2. For a moment push away a scooter handlebar simultaneously stepping over folding activation
lever arm — the latch have to be released out of a slot
3. Fold the scooter handlebar
4. Attach it to rear brake wing

You can also find a video how to do it here: https://www.youtube.com/watch?v=B1Puv_cLVv0