Hello! I have a lot of experience with Salesforce and Sheets...What’s not working here, as the process you described should work:

We were hoping that every time a new spreadsheet with the data was created we could simply pick that up and bring it into Salesforce as the columns are always the same. However, we haven’t been able to to do this.

What happens here - Do you have an error we can see? 

We then thought that we should create another Zap in order to take the data from the “new” spreadsheet and update a “master” spreadsheet which could then bring the new rows into Salesforce. However we  can’t seem to be able to do that either.

What happens here? An error/screenshot would also be helpful

Hey @Gareth! Just checking in here to see if you saw Andy’s reply and to check to see if you’ve solved the issue or if you’re still running into problems. Let us know - we’d love to help get you pointed in the right direction, here!