It automatically resets when fault is no longer detected. It is an old system and I do not belive it retains much information. The ECM is much like the ABS system.
If you mean the Oxygen Sensor light, comes on every 50,000 miles, look under the left rear seat. You should find a computer module with a pushbutton on it. Push and good for another 50,000 miles.
At least on my 85, and 84-88 are the same in the book, but then, mine was the 5000.