So your base field is F=k(I) where . Now consider the splitting field for an irreducible polynomial f in k(I) such that , where (verify this). We see that .
Now we shall find an intermediate field corresponding a subgroup of . Let . It is easy to check that H is a subgroup of . The field corresponding H is , which is fixed by elements of H.
I'll leave it to you to find all other intermediate fields, because it seems like a lengthy computation is required to find and verify it.