Where is the blend door actuator located?

That would be the mode door not a blend door. It is on the end of the HVAC housing above the drivers footwell. You need to remove the knee bolster under the steering wheel, then remove the floor duct that attaches at the case. Now you can get to the actuator at the end of the case. Replacement is to just remove the screws and swap the actuator. Then you need to reset the actuators. With a scan tool this is easy, without one you need to pull the HVAC/ECAS fuse and keep it out for 20 seconds at least.
Now install the fuse and turn the key on and start the truck. Wait about a minute while the actuators recalibrate. Now test the operation of all the actuators.