There's no need to. One simply reads the instructions and transpose the wires for the spdt relay from the Digistat.
Dan I wouldn't waste your energy with him, he's an idiot.
If it's a New Build OP & you don't get the installer or Electrician to fit your 'Nest' you'll f.ck up any warranty on your whole installation. If you have problems with your CH system they'll tell you to do one.
Advise the Google Warrior didn't give you, cause he's just that.