If it was bought with a computer in the same order, you will need to provide the computer's Service Tag. If it was bought separately, you will need to provide the order number and a copy of the invoice. Details here: How to get support for your Dell Keyboard and Mouse that is still under warranty. 
Hello, I want to claim warranty of my mouse Dell MS 116 Mouse. It's still under warranty. Also, I can't find any service tag for my mouse. How can I proceed?
I want to claim my Dell MS 116 Mouse Warranty