I have got an Irish low-whistle in D, and have been searching on the internet for the fingering for the higher C, but have been unable to find a working one anywhere. I also tried experimenting by myself, trying to approach the sound, but never managed to get a decent one.
The internet yielded different results, but none could give the note I was looking for. I don't know whether the fingerings were not the good ones or whether my whistle is not good enough. For your information, it is a Susato low whistle in D.
Could any of you give me a good reference on how to play this higher C?
Here is a finger chart that exactly shows what I have:

The note I need the fingering for is the higher C on this chart, which would be C5 - I think - since this chart is for a tin whistle and the low whistle I have plays one octave lower.