If you want to make changes to your data, one method is to exporting data into an Excel file, clean up your data locally, and then reimport the data back into Dynamics 365. If you do this, there are a few things you should keep in mind:
- Even though you’ll save the file you export from CRM to your local drive, do not reuse it. Make a new export for each import you plan to do. The exports are for one-time use only.
- All the unique identifiers for a record are stored in the first three columns of the Excel sheet. These are hidden. Do not attempt to change data in these columns, or CRM will not know which record to update.
For more details and a walkthrough on this excel reimport in Dynamics 365, refer to this blog on how to mass edit records using Microsoft Excel.