Oxygen sensor advise

I've got a 2010 Tacoma V6 Prerunner with 66,000 miles on it. A few days ago my check engine light came on as well as the anti skid light. They weren't blinking. I called a dealer and was told it might be a "gas cap" not clicked in. I was told to check that and give it a few days and those lights would probably go out. It's the third day and they're still on. I stopped at AutoZone and they hooked up their diagnostics. According to that my #1 oxygen sensor is the problem. So it looks like a trip to the dealers for me. But, I thought I'd get another opinion hopefully from someone here that has had the same situation. First of all, where is this sensor located? Is there more than one? Is this something an average do it yourselfer can change? If so, how do you reset the computer, or will it correct itself once the sensor has been changed?

Any help or direction would be appreciated. Thanks.