AUTO WIN is the option to play a mission instantly and receive its rewards without actually going into combat. In other words, it's the quick and easy way to acquire the rewards without spending the actual time playing.

This option is only available after you have already beaten said mission with 3 stars.

If you have not cleared a mission, or you cleared it with 2 stars or less, the AUTO WIN button will be grayed out and unavailable.

Note: AUTO WIN requires the same number of Campaign Energy as playing the mission manually.