Here’s a brief recording of me playing the opening lines of “This is my Father’s World” (Terra Patris) on my Triplett Luna harp:
For comparison, here is the original hymn in four parts. I transposed it to F so it would work better on my harp.
As you can see, I took just the top line (soprano), which is where the melody sits.
After you get comfortable playing the melody you can add in harmony, either from the original hymn or by ear.
I used MuseScore 3 to typeset, transpose and print the new version of the hymn.