Hi Again Martina,
When you are Updating records by Importing the Records back into Method, you need to ensure that you have the Update existing records by matching the key fields option checked when preparing the data as I mentioned in my original Post.
There really isnt a quick way to Delete duplicate records once they are in there. If you still have the Table containing all or Opportunities, the quickest option for you would likely be to Create a new screen with an action to Look through the Opportunities Table and utilize a DELETE FROM TABLE action to remove all existing Opportunities, and then Re-Import your Current List of Opportunities the same way you did the first time.
What I might recommend at this point however, would be to have one of our Consultants take over and complete any updates/Importing you need done. I can have your Account Manager reach out if this is something you might be interested in.
Thanks Martina!
Regards,
Ben