You probably can't because it may already be tied to someones account. You'll need the person's last 4 digits of their social security number, and their zip code to activate it. You should do the right thing and try to find out who actually owns it and try to return it to them. I'm sure they'll be very happy and who knows maybe you'll get a reward. Even if you don't get any reward other than a thanks it's still the right thing to do.