Apologies as I could just be confused here.
You said
The process is when a microsoft form is completed, this triggers a flow to add the details of that form to a row in an excel spreadsheet. I then want to be able to create a copy of the file and when that is done for another flow / trigger to delete all rows in the online original file.
What does "I Then want" mean. As in, when is when? An hour later, immediately after you add the row?
So every single time a Form is submitted you want the file copied?
Curious why don't you just put the data in the location you want it, versus adding it to Excel, then copying the rows to another file somewhere else, then removing lines?
When you say you want it when you do a Copy Download. Is that done manually or via some flow or App?
If it's done manually, then you would have to create another flow.
in that flow, you would trigger when a file is created
Assuming you are using the same file name OR can parse the original file name from the new name OR you have it in an environment variable or other configuration, then you would use this trigger, to go back to the original file and remove the rows.
If I can make a recommendation though.
In the original file you should have a DateTime Stamp and only remove lines that are before the File Download or you might remove new lines that are generated in between the file download and the original file update.
If these suggestions help resolve your issue, Please consider Marking the answer as such and also maybe a like.
Thank you!
Sincerely, Michael Gernaey