I have a 1990 Buick Riviera need to replace heater core where do i start

Okay you want to know what you are getting into???? Honestly its a complicated task with numerous steps. Hope you have the time and patients. The heater core is located inside under the dash in front of the console if it has one. First you need to remove the console and then the heater core cover. This task requires many different size tools mostly small ones. Once you remove the cover there are several clips holding the core in place. Then you have to go beneath the vehicles' hood and disconnect the two core pipes/lines and you should be able to remove/replace the core. In order to remove the console use needle noses pliers and remove a small U clip front of the gear knob and pull upward removing the knob. Good Luck>>SEMPER FI