92 PA Change Oil Soon Reset

Greetings,
I own a 92 PA and I need to reset the 'Change Oil Soon' indicator. It's not like the 94 model with the button in the glove box. How do I reset this and exactly where is the location of this reset button or slot? When I had the oil changed the service guy didn't reset it. Also, I'm no auto mechanic. I try very hard to take great car of my vehicles but what's the truth about motor oil and my question is this. I was told there's conventional and synthetic oil. The guy talked me into going full synthetic this time and stated that I would not have to change my oil for 8000 miles. Is this true? I've gone to two separate Buick dealerships and the both had something totally different to say about the oils and how often I should change it. But then I hear that the conventional oil can last much longer than the average 3000 miles if the engine is in top running condition with high mileage. With the price of gas nearly $5, it seems that the auto industry is taking advantage of auto owners in various ways. I used the Mobil oil brand because the tech said it's the best and that there would be no sludge with synthetic oil. My car currently has 110000 miles. I live in AZ where the temps are 'muy caliente'. Your help is appreciated.
Thanks

The reset button is in a hole under the dash on the passengersside, near the door.
You have to press it for 5 seconds with a pen. It will then blink 4 times to confirm the reset.

If the button is not where it ziggy says check under your passenger side door as well. I have the same car and mine is on the bottom of the door.