How do I set up 2 TVs with one Apple TV?

I expect you're asking if it's possible to share the output of 1 ATV to two or more TVs. Google "HDMI Splitter".

A device that splits 1 modern HDMI 2.1 signal for 2 outputs costs around US$40. Plus buying decent HDMI cables of sufficient length and running them neatly where they need to go... You may be better off buying 2 ATV devices as @ckuan suggested :-).

You can't.

You need to buy another one.

HDMI Splitter

Then both TVs get the same picture, not independent programming. Should be mentioned.