How to add Google credentials to Cal.com?

I have installed Cal,com and so far so good.

I attempted to install the Google Calendar addon and I was greeted with an error message.

It seems I need to set up my Google API credentials.

I found these two links:

The links above explain that credentials need to be added to the Cal,com .env file, but being new to self-hosting, I have no idea how to access the .env file from within CasaOS.

Please can someone tell me what I need to do to edit the Cal,com .env file?

Thank you.