Using UE5 Modelling Tools to Cut a Static Mesh Collision

Please can someone tell me why when I use the Polycut tool in Modelling Mode to cut a static mesh to the correct size I need, why does it not cut the collision box aswell?

If you can see in the screenshot, I cut a roof tile mesh so I could slot it in, but the collision box is still the same size.

Please can someone tell me how to cut the collision aswell?

Thanks