C penny whistles are a mater of length, slightly longer than than the more standard D whistle, but not as long as the Bb whistle, etc. Stanza mean verse and all stanzas are the same musically. The counterpart of the stanza is the chorus. The 1st Noel chorus is very similar to the verse. However, everyone likes to sail up to the high note near the end of the chorus. This is actually usually the tenor line in most 4-part hymnal arrangements.

Below are the fingerings where "1" = one finger down on the first hole and "6" = six fingers down on all six holes, other notes etc, 0 = no fingers. When you need to overblow for the upper octave I'll add an * asterisk. There are no odd fingerings needed to alter the basic scale. On a C whistle, your tune will be in C, on a D whistle it will be in D. I'll assume you know the rhythm.

Verse (or Stanza).
4 5 6 5 4 3 2, 1 0 6* 0 1 2, 1 0 6* 0 1 2 1 0 6* 2 3 4,
Repeat this line again and you have the entire verse.
Chorus
4 5 6 5 4 3 2, 6* 0 1 1 2, 6* 0 1 2 1 0 6* 2 3 4,

Chorus with the soaring tenor line
4 5 6 5 4 3 2, 6* 0 1 0 6* 5* 4* 3*, 6* 0 1 2 1 0 6* 2 3 4,

This should answer your question. However, tunes were made to be changed. The 1st Noel is really nothing but playing the scale, with a few breaks. Sink into the tune, play it anyway your mind desires. That's why everyone sings the tenor line and not the tune. They love it. There's no such thing as correct and I'm sure there are many yet undiscovered variations waiting to be sounded. Enjoy!