In case anyone was actually looking for help with 2 wave fights, as already noted it's a good idea to go manual. Take every advantage of terrain effects. Minimize further damage to an injured unit by moving it back away from the action - keep it alive for round 2. Use your units to gang up on one enemy unit, and don't leave the injured enemy unit alive to take a second shot at you - finish it off. The basics.
Main thing is to minimize your own damage and survive intact enough to win the second fight. Knowing what you will face in that second fight can temper what you do in the first one. It was about a year's playing before I discovered that (on mobile) I could tap the second wave tab and SEE what was coming. Well now that's mighty nice stuff to know lol!
Everyone will have different favorite units and combinations but to illustrate the idea: Colonial Age, 1 heavy, 1 light, 6 rogues, fighting manually. The light unit has good movement and can chase down ranged units and get across the field quickly to dispatch enemy artillery, but it's fragile vs enemy heavies. My heavy is durable but has less movement so it can get chewed up by enemy ranged and arty units. If the second wave enemy army has a lot of arty, I am really going to want a healthy light unit in that fight capable of taking them out. So I will often place my real light unit in trees and hide it until the first fight is basically done, saving it for when it counts in the second round. Fighting with rogues is a topic in itself.