When you have the custom Excel setup open, you can use 'Options' in the top right corner to duplicate or delete the file.
Duplicate
Click on the custom Excel file name to open. In the top right corner, go to 'Options' and choose 'Duplicate'.
The formats and content will be copied, as well as the title. However, there will now be a number added to the title, such as "Worked hours 2".
The new file can be edited with no impact on the original file. Use the menu on the left to make changes.
Delete
Also go to 'Options' if you want to delete the file. Deleting is permanent. You will no longer be able to create a new export with that setup. Previously created Excel files will no longer be available and are also removed permanently.