In Disjunctive Normal Form, all terms are seperated by disjunction.
We know that A→B = ¬A ∨ B.
Therefore, R→S can be written as ¬R ∨ S.
The whole equation now becomes,
(~P∨~Q) & ¬R ∨ S
Further,
(~P & ¬R ∨ S) ∨ (~Q & ¬R ∨ S)
This is the Disjunctive Normal Form.