In this video I will show you how to the uncorrupted angels in Eden Prime. Now this can be misleading, because this is in the level called Bastion's Fall. It's right after the fight with Astarte in the level Eden Prime. So don't get that mixed up.
As you continue wit the level you will be forced to stop and fight some corrupted angels and baddies. Once that is done you will then jump down to a lower level. You will see two uncorrupted angles with regular white wings. Make sure they stay alive. They also have health bars, so pay attention to that. Once you kill all the guys in the area a dialog will happen with the good angles. Then you will get your achievement.