Moto button, back and task list, is there a gesture for back in nova

I like the Moto button to use for home and ok Google and locking screen but...

I find the that the left and right gestures are hard to do so I came up with a work around.
I use nova desktop site I set the swipe down action to be task list but I can't find a gesture or shortcut that I can use for back.
If I can see a shortcut then nova should be able to add as a gesture. Does anyone know how to make a shortcut for back?

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