When [oh-] changes from 10-9 to 10-11 in a solution:

kw = [h+][oh-]

what is the [h+] after the change?

According to the fact that  [H+]*[OH-] is always equal Kw, you can easily find concentration of [H+] by changing from to 
H increases, Kw is constant, therefore 
And you will have  where pH is 3