If you don't have anything, don't write anything. It'll look better to be honest than writing down something that's an incredible stretch.
Honestly, putting a puzzle together doesn't seem to really have anything to do with the kind of manual dexterity the application is asking for. Spatial reasoning? Sure, but not manual dexterity.
Here is a list of things that require manual dexterity:
Tying flies
Sewing
Knitting
Macramé
Crochet
Painting
Sculpting
Carving
Jewelry making
Calligraphy
Playing most musical instruments
Video Games*
Tattooing
Model Building
*This is proven by research in the surgical AND dental literature. That being said, I wouldn't include it on your app. Mostly because the older generation (People who will be interviewing you) still associate this kind of activity with laziness, and some experiences with video gaming is almost universal in our culture at this point, making it not very interesting.