**** WARNING **** As a best practice, it is highly recommended that you export the contents of the table before you update it using the DataLoader. This will allow you to revert back to your state before the update.
You can use the DataLoader to change the due date for the tasks.
1. Export the tasks you want to update using DataLoader from the Task table. You'll need to make sure you include the following fields:
NOTE: The Id value is required when you update a record in the Task table.
2. The exported file from DataLoader will be saved out into a csv file. Locate this file and update the ActivityDate value for the records you want to change.
3. Save the changes.
4. Open the DataLoader and choose "Update".
6. Click Next.
7. Select the "Task" object.
8. Click "Browse".
9. Navigate to folder where the csv was saved.
10. Double click on the csv file to select it.
11. Click on "Create or Edit Map".
12. Drag the ActivityDate to the bottom section to map it up to the ActivityDate column in the csv file.
13. Drag the Id field from the top section to the bottom section to map it up with the Id field column in the csv file.
14. Click OK >> Next >> Finish
15. Click "Yes" when prompted with a pop-up message:
You selected to update existing records. The action you are about to take can not be undone. Are you sure you want to proceed?
16. Click on "View Success" to view the results.