Hi Canadian Bob, from Puerto Plata, take Rte 5 to Navarette. Turn left and take the autopista to Santiago, arriving at the northwest corner of the city. The autopista ends at a circle. Turn right at the circle. This becomes 27 de Febrero (if you keep straight, you would be on Estrella Sadhala). Go a mile or so, passing a Republic Bank on the right, then a Texaco and McDonald's on the left. Go down a hill. At the stoplight at the bottom of the hill, Las Colinas Mall will be on your left.
(Other posters please help here--here's what I would do). Make a U-turn at the light, then take the first right into the parking lot in front of the mall on 27 de Febrero. When my wife and I went to the mall a few months ago, we drove all the way around it, but found no other open parking lots. That may have changed by now.
Hope this helps, Bob