How do I fix an EGR valve on a 1988 Buick?

I have a 1988 Buick Lesabre that has a couple engine codes. The first one is for a failure of the EGR valve. The second is for the oxygen sensor. According to the guy at AutoZone, if I fix the EGR the oxygen one will go away. Problem is I don't have a Chiltons manual or the specific knowlege to find and fix this. I have mechanic skills just not the book and info.