js source file has been changed to created in cs.

The question seems to be: - "A previous script written in js has been replaced with a new version in c#, but the editor does not recognize the new version as being the same object, so everywhere the old script was used now says 'missing script'. How can I have the new c# script recognized as a replacement for the previous js version?"

Sadly this is one of those apparently obvious items, with no automatic solution, so you will have to do this for every location and every gameobject where the old script was used.

In the editor, in the inspector window, click on the round icon to the right of the "missing" script name and select the new script from the pop up list.

If you have a lot of scripts in the system, you may find it easier to drag the script from the project window onto the correct position (where the "missing script" message is) on the inspector.