How do I get the Motor6D C1 offset in terms of it's C0?

I am coding weapons to aim up and down with your camera. By doing so I have to shift the C0 position to CFrame.new(0,1.5,0), which is the position of a character’s head (and the position of the 1st person camera), so that when I multiply the C0 by an aiming factor it moves up and down with the head, up and down with the camera.
That being said the weapon itself shifts up. To counter this, I have to move the weapon down, by manipulating the C1 value. However I do not know how to do this; I cannot simply write C1 = C1 - CFrame.new(0,1.5,0) because that would move the weapon down in its local position. I need to find the offset in terms of C0.
Does anyone know any methods to do this?

I barely understand, so what you are trying to do, it’s to return the offset in object space?
Between C1 and C0?

Yes
Assume that C0 is CFrame.new(0,1.5,0)
I am trying to move the C1 back to it’s original position of CFrame.new(0,0,0)