I am reading a note at Page 63

ftp://ftp.math.ethz.ch/users/pink/FGS/CompleteNotes.pdf

It says whenever $G$ is finite and flat over $S$ the functor ${\rm Hom}(G,H)$ is representable. But it does not give the proof or any references.

Can anybody help me with this question?

[The original statement][1]

  [1]: https://i.sstatic.net/eKDQN.jpg