How do you know which O2 to replace and where are they located?

The Oxygen Sensor codes are numbered i.e Oxygen Sensor malfunction Bank 1 Sensor 1, Bank 1 Sensor 2 etc. If a parts store did this scan, I would take your car to a Pro shop, because I see many, many cases where the Parts Store does not even understand what the code says or means and people spend thousand and get no where. the fact that the person who read the code did not even know what ( B1S1, B1S2, B2S1 etc ) is already a red flag to me.

I have 137000 miles on mine. It did the same. The mechanic told me to put some good gas in it and drive it on the highway. Take it on a trip. The light hasn't come back on. Good luck.