Sure. Thank you!
The Dam mission is a remake of the first level of Goldeneye for the Nintendo 64, so it's more or less a nod to those who have played the game. I would need to write an extensive guide here, so instead of that you can check this walkthrough by the excellent graslu00:
You spawn reinforcements with the G key in your keyboard. The reinforcements that will spawn are the ones that you assign to the combat ready list in the Institute (the area you start the game in). Use the Character Management terminal to do that.Sorry for the lack of clarity. As weird as it may sound, I don't always have the time to make tutorials.