You could try using standart-game AI scripts "Melee game - Run AI".
If that doesn't work (the AI moves units or anything else), you need to create your custom AI.
Just go to the AI editor. It creates new AI on start, just rename it, delete everything in "Attacking" tab, and use File -> Add to map.
Then use "AI - Start Campain AI Script" and put in the name (including import path)