Changing Walkie-Talkie Talk Setting

I'm stumped.

At some point - somehow - I changed the Walkie-Talkie watch app setting from the default "tap and hold to talk" to "tap once to start talking and then tap again to stop talking".

I thought this would be a good idea at the time but after accidentally broadcasting to my daughter for several minutes this morning I'd like to go back to the default setting.

I've looked under walkie-talkie on the phone's watch app - looked under settings on the watch - hard pressed in the app - can't find where to change it back. Can't find it using Google either.

Any hints anyone?