Hi @jbaggs, welcome to the community 
I assume your problem is with writing the updated value, not so much the reading part, right?
This is a bit tricky as n8n’s Google Sheets node does not let you write into a specific cell. So you would have to make the required API request through the HTTP Request node. I’ve shared an example of how to so over here.
Hope this helps! Let me know if you have any further questions on this.