All you need to do is to understand AIs' mechanics and basics of the game. First of all, I would recommend you to learn about orders' priority (when to attack with a first/last order). You can beat this challenge easily with only this knowledge, the more advanced method would be to use delay moves (the technique which makes your last attacks to be very last). These are the tips for every single player level, if you understand the basics of the game, then you could beat AIs in a few tries.
To learn about it more you could read any of the strategy guides that players offer, for example http://tinyurl.com/MH-strategy-guide
Edited 7/27/2017 09:32:41