How to change focus of a Haskell Store Comonad on a 2D list

Question

I am strugling with the following problem. I am trying to make Game of Life using store comonads in Haskell. I have the following relevant code:

type Cel = ((Float, Float), Bool)
type Field2D = [[Cel]]

I have then created an initial field:

initialField2D = [[((0.0, 0.0), True), ((0.0, 1.0), True)], 
                  [((1.0, 0.0), True), ((1.0, 1.0), True)]]

The initial field is a small example where I want to test my program on. Now here comes the tricky part.

initialStore2D :: Store Field Cel
initialStore2D = Store (head.head) initialField2D

f :: (Store Field2D Cel) -> Cel
f (Store f s) = cellUpdate (f s)

cellUpdate :: Cel -> Cel --Simple trivial cell update function that just moves one spot.
cellUpdate ((x, y), a) = ((x+1, y+1), True)

newStore = extend f initialStore2D -- Apply the update function to every cell.
extract newStore --Correctly returns ((1.0, 1.0), True)

Now my question is, what is a good way to change the focus onto the updated store? Moving down is simple:

goDown :: Store Field Cel
goDown (Store f s) = Store (f.tail) s

My question is, what would be a good way to move right or left for example? Did I chose a bad index function (head.head)?

Thank you for your time!