You can shift the whole envelope up/down.
I'm not 100% sure of the correct way to do it, but with the entire track visible and the track maximised (best to do this in the parent track because you can make it higher than a take lane), click & drag in the lower half of the track to highlight a range (make sure it encompasses the entire envelope), then move your cursor to the top until it turns into and up/down arrow separated by an I-beam on its side, then click & drag up/down.
It takes far more time to write down than actually do it