At least for ZHA, the switch to switch How-to instructions are just a copy of binding a switch to a bulb, so they’re somewhat less than ideal. Plus HA has changed the UI a bit. I assume the instructions are just unfinished. (@Eric_Inovelli: Any ETA on having instructions?)
FWIW, Here’s what I did in ZHA:
On the device page for the switch, click the three dots in the Device Info section, and choose Manage Zigbee Device.
Select the Bindings tab.
Choose the other switch under Bindable Devices and click Bind.
(At least for me, the spinner never stopped spinning, but it seemed to work.)
You’ll then need to go to the device page for the other switch and repeat the steps to bind the other way.