You find the commond in your General's Garrison and will be highlighted when it can be used.
This is of most use when:
- Intercepted by an unseen or unexpected incursion into an area of effect.
- Attacking the wrong target.
- Attacked with the wrong General
- Retreating from an attack after getting deliberately distracted.
As soon as you wish to retreat you have to reopen the Generals Garrison and click Retreat.
Server lag often means it takes a few seconds to be actioned but in most cases it is honoured at the time of pressing rather than when the game client updates. This leads sometimes the retreat visually failing and your General starting his attack only to suddenly appear on his horse and heading home.