[Haskell-beginners] Updating lists inside another list

I have a list of pairs. Each pair has a value and a list. So, the structure looks like this: [ (a, [b, c]), (b, [a, c]) ] What I want to do is be able to add an element to the inner list of the pair with the head value of my choosing. So, for the above list:

addToInnerList [ (a, [b, c]), (b, [a, c]) ] a d [ (a, [b, c, d]), (b, [a, c]) ]