resetting a 1991 buick roadmaster estate wagon hearse?

[Pilot]

I asked this question once, but I am not looking for anyone opinion, I am looking for the answer otherwise I would not be asking the question right? I need to know how to clear codes off of a 1991 Buick Roadmaster? It is a 1991 Buick Roadmaster Estate Wagon Hearse. The ABS light is on. I have disconnected the negative, then the positive, then both, and left them off for over 5 minutes. I have also tried turning the key to on, then pushing the accelerator 3 times within 5 seconds. Now I have added brake fluid. The car sat for 2 years or so not driven. The brakes work fine sometimes a squeel here and there, but it has been siting for a few years give it credit. Diagnostic test came up with nothing, no wheel bearings grinding. So in conclusing I am not looking for someones opinion, I just want the answer! How do you clear this code or any codes in the vehicle for that matter. Obviously if it continues there may be a problem, I think then I can figure that out for myself. Not trying to be rude, but sometimes even when you spell it out to someone what you are looking for, they still don't have a clue. And if you want to give input on how to get better gas mileage since its about 20 gallon tank and so far it only going up slowly to about 10 miles a gallon or 200 a tank on its 3rd fill up for a few years. I added injector cleaner already. Any thoughts on this?