With the effects set up as default and assuming you have the that reverb you want already dialled in.
1 Press the upper layer key to access the 3 stereo channels, FX returns, FX sends and Mix masters.
2 Press the Mix 7&8 key on the right of the desk.
3 Push the fader for FX1 RETURN (it’s the 4th one) up until you’ve got enough.