When you click the rates in the Global menu that sets the base rate that all 5 channels will play by default, but it only changes when they’re next triggered so there’s a smooth transition - there’s 4 rates, all an octave in difference to keep things in tune.
Each channel has a context menu popup (labelled ‘fx’), from there you can choose other rates which will randomly trigger:
1.0 is original sample 0.5 is half speed/pitch 0.25 is quarter speed/pitch 0.125 is 1/8 and not suitable for most things you’ll sample as it’s very low
the base rate should be greyed-out and unselectable.
I’m working on a new ui for this now which will hopefully be less cramped and easier to work with - with lots more features too.