Disclaimer: I'm no expert and I'm not a "natural" musician - I'm struggling, too.
But I don't think there is a "magical switch". Only hard work and small improvements over time. Have you had a look at YouTube? There are six beginner lessons from the OAIM (Online Academy for Irish Music) where the teacher not only plays the piece but also shows very clearly which fingers move and she even says the names of the notes. Playing with her seems good preparation (I hope!) to picking music up by ear alone (now if only I could remember what I played yesterday...). Also on YouTube is Ryan G. Duns ("a jesuit's tin whistle lessons").
And of course, as DrPhill said, if you can hear the melody in your head, half the work is done. I find that much easier with songs (as opposed to tunes) - I can more easily remember a melody that's "tied" to a text (like Duns's "Roddy McCorley" - a new lesson 1 (
https://www.youtube.com/watch?v=RlQYpnLILPc)
Does anybody here have a source (YouTube link...) for tunes played slowly and without ornamentation, but without necessarily breaking them up in sections and especially without lots of talking in between? I'm ashamed to say that by the time I've finally played part 2, I've sometimes forgotten how the first part went
