Is there a left handed set up or does it even matter?
Apple Watch
There is a one-handed keyboard option in Settings>General>Keyboard. You can select either right or left. I've never really used it so I can't say how useful it might be.
I'm a lefty and I never had a problem using iPhone.
It shouldn't matter. I'm not aware of there being a left handed setup. A similar question was asked in 2016, and the best answer was to send feedback to Apple at http://www.apple.com/feedback/.
Here's the similar question: https://discussions.apple.com/thread/7506485
Left handed set up
