S Memo has disappeared from my phone, how can I retrieve it with the notes in it?

[AC Question]

I have a Galaxy S4 mini and a few days ago the S Memo app just disappeared. I have checked in Application Manager and it isn't listed now.
I didn't delete it (I don't know how to delete) so does anyone have any idea what might have happened and if I can retrieve it along with all the important notes in there?
Lynne