What should I do with my Toyota Camry 2004?

I have a '04 Toyota Camry with 80,000 miles on it. I was hearing a noise when I start ignition one day and I took it to my mechanic to inspect it. He told me that everything is fine except for the Flex Pipe. So I took it to Meineke to get it fixed. The next day after the fixture my check engine light came on. I took it Auto Zone and I got Check engine code P0035.What should I do with my Toyota Camry 2004?And what does code P0035 translate to? The people at Auto Zone have the book to tell you what the code is. I bet it is an O2 sensor

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