To access them, you'd have to remove the transmission from the vehicle and disassemble it partially. This is a significant job requiring specialized tools and knowledge. It's not a task for the average DIYer.
There are several different solenoids within the transmission, including shift solenoids and pressure control solenoids. Their exact location *within* the transmission varies depending on the specific transmission type used in that year Grand Prix (there were a few possibilities). A workshop manual specific to your car's transmission is necessary for precise location.