bought "open Box" macbook air, 2010, received n...

We bought an open box, model A1370, 11 inch 2010 core 2 DUO, 1.4Ghz, 64 GB ssd, at Best Buy in 2011. Loved it.

Am preparing to sell it and have discovered that I did not receive the thumb drive to restore it to factory. I did not know one was supposed to come with it as there was no booklet or anything.

I want to remove all of my data and factory reset it. Can someone help me please?