Hello Gerard,
Hope you're doing well.
Here's the steps to open the Extensibility Configurations property:
1) Open your module in Service Studio (like you already did).
2) Go to the module's properties. In order to do that, you just need to click in the module itself.

The properties will open in the bottom right corner:

3) Scroll down in these properties until you find Extensibility Configurations property:

4) Double click to open it:

Hope that this helps you!
Kind regards,
Rui Barradas