Dear Kelly8766,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
From your description It seems you want to know Removing Someone's Write Access in SharePoint/Excel.
I have carefully read and understood your query. As a community, we are here to provide suggestions and guidance to assist you. However, we do not have the necessary permissions and tools to perform any back-end testing. From your limited information, I am unable to narrow down your requirements can you try below basic troubleshooting methods below and tell me your result?
- Please go to the file >> right-click on it >> manage access >> stop sharing.

- Please go to the file >> right-click on it >> manage access >> click on 3 dots >> advanced settings >> select the user >> edit user permissions>> read-only.



Your understanding and patience will be highly appreciated.
If there is any misunderstanding, please feel free to correct me.
Have a nice day!
Best Regards,
Sophia