Sadly a lot of bike user manuals are generic to handle every model of bike. So they have a lot that doesn't apply to specific models. I don't know if that is the case for Cube bikes though.
I did see that some models of the Cube bikes did have a way to adjust, but the promo video of what I think is your bike didn't look like there was any method to tighten it short of just slop between the axle and the drop out.