How do I trigger an email based on the excel sheet response , i.e. if the column d input is less than 40 then that person will get an email ( email if in column c) .
Now this file will be saved in onedrive and will get updated monthly.
Excel triggers donot run on a row update.
You can add a trigger on file modified, then retrieve the rows from excel.
Add a filter to get the rows where ColumnD<40.
Add an email action by specifying the ColumnC value.
It will be much easier if you convert the excel sheet into a SharePoint list. That way you can track each row separately.