Changed Spark Plugs Today

[FlyingEL]

Was a good sunny day and I decided to change my Spark Plugs. Got the Iridium IX plug from EBAY at a bargain ($68). During changing the plugs, the Air filter system got to be taken out. Some wiring was unplug to reach the spark plugs.

1st finding: The OLD Plugs were very worn out, glad I change them.

2nd finding: The plug nearest to the passenger has some old on it when I pull it out. IS there a problem?

3rd finding: Car was much smoother after the change.

4th finding: The Engine check light came on after the plugs changed. I guess I unplug something I shouldn't have. But car was fine to drive. How do I reset the warning?