You learned the tune. Now take it up a notch!
Any of these third harmonies will work when you are playing C shapes.
Here are the riffs I utilized in the video:
Riff 1 ("This is my...")
There are plenty of other riffs you can do based off these ideas. Once you feel comfortable with these, try them along with Matthew West's "Blessed Assurance (My King Is Coming)" then incorporate the same riffs into these other lessons. In fact, since the chords on "Set A Fire" are so repetive, try fitting the melody with third hamonies and combine them with the chords. Have fun. As always, I'll take questions or comments below. Get to work!