You can't. Generally, an honest person will just destroy the card or call the number on the back to report it missing for the person who owns the card. Don't be stupid, it is very easy for a bank to track someone who is using a lost debit card.
How Can I Use Found Debit Card?
Please call the number on the back of the card and return it to its rightful owner. I'm sure you'd be upset if you lost something of value...thank you.