How do you reset the timing gears on an '89 Lemans 1.6?

If you mean by "timing gears", putting on a new timing belt then it's easy: The top sprocket has a line etched in it. This line should be at 12 o'clock. The bottom pulley also has an etch on it also, this should be lined up at the little black pointer (located about 2pm). The trick is to tighten the belt so that when it's tension is correct, the top sprocket is set at 12pm and the bottom pulley line matches up with the black pointer.

One thing to add to get the belt on you have to loosen the three Allen head screws that hold the water pump in and turn the assembly in order to get the belt on and then twist it back to take the slack out of the belt. Once you do this reset the screws and you're done.