I purchased a device that came with an SD card. I need to return the defective device and along with it the SD card that came with it.

Of course like many I am concerned about identity theft and want to be sure that all the information that I had on the card like tax info, business info, spreed sheets etc are completely destroyed to the best of my ability. I don't know where that card will end up next once I return it. The card that came with the device was a large capacity card so I used that card for my person information and other SD cards that I had that had less capacity for the device. So I need to return that specific SD card.

Are there any good file/SD shredding programs available for free on line that I can use to destroy the contents? I have AVG anti virus and it has an option in the drop down menu (in file explorer) if I right click on a file to shred the file. But I have written to this SD card and deleted files already multiple times so that won't do me any good. I need something that will totally wipe the entire SD card completely. I know just formatting it won't give me the results I need.