how to reset the check engine light on a 2004 kia spectra gs hatchback

What is your question?

My 2004 KIA SPECTRA GS HATCHBACK recently had it's battery replaced. Once the battery was replaced the check engine light went off. A day later the check engine light was back on. I was told it was the O2 sensor on the passenger side but it was unclear if there is a blockage. My check engine light did not turn on until the battery in the car ran out of juice. How long have you had this problem? A few weeks.