Hi Lisa, I searched high and low for a full tutorial to show you how you can make one, and the best I could find was this article here - https://www.recyclart.org/old-treadle-sewing-machine-converted-singer-chair/ It should give you a basic idea of how to go about it.
Hope this helps it takes a minute to load (lots of pics)
There does not seem to be many tutorials out there for chairs. If you look at this picture it will give you a good idea on how it is done. Just change the design to suit your needs and taste.
Number 5 under this link is a suggestion on how to make a chair from a trundle sewing machine base:
You could buy a thrift chair and swap out the base
Lots of photos here