The easiest way it to choose the fps template (with the blue weapon) - delete the skeletal mesh and the shooting part of the bp - choose the right gamemode in the world settings -> now in the character bp you can change the eye height 
The easiest way it to choose the fps template (with the blue weapon) - delete the skeletal mesh and the shooting part of the bp - choose the right gamemode in the world settings -> now in the character bp you can change the eye height