you all shouldn't talk bad about someones lack of knowledge, alot of people don't full understand the electronic systems in the automotive world yet
you could have the codes read by the auto parts store or do it yourself, but i would first start with what agent said to do, anytime you work on something and it causes a problem the first thing that should always be done is retrace your work
in your case make sure the plug wires are in the right place, make sure they are snapped fully into place, and make sure that the plug gap is correct