Hi @maria74824

There are two O2 sensors in the engine. Which one do you want to replace?

Here's a video that shows how to replace the downstream O2 sensor and another video that shows how to replace the upstream O2 sensor.

I just had the same thing happen, and I think I fixed it! The two little black pieces cover the lens when not in use. There are little holes at 12:00 and 6:00 (as if you are looking at a clock). The little black pieces have notches that fit in the holes, and the two pieces fit together like puzzle pieces (almost like a yin/yang symbol). The larger black piece that is more square sort of snaps in over top of those. There are guide holes. Then the lens part snaps back on. You might have to fiddle with it to get those two small pieces to fit, but it should work. Good luck!