Which file should I modify to add additional button to image viewer page?

I need to add an additional button to image viewer page which opens a radiology report editor in our app, but I am unable to locate the file to modify for doing that.

I am using OHIF version 2.0.0

The OHIF toolbar buttons are located at /extensions/cornerstone/src/toolbarModule.js
You can modify which toolbar buttons appear and where they appear.