how to reference a js script attached to a prefabs child from a c# script attached to another prefab?

Hello.

I have a prefab with a child object. This prefab has a child. Attached to the child is a .JS.

I also have my player prefab. I have a c# script attached to the player prefab which I need this to communicate with the above mentioned .JS script.

Can anyone point me in the right direction to achieve this please?

Many thanks.