Need a manual fix to open dash air vents. on 2002 Cadillac DeVille DTS

Mode actuator switch needs replaced and I understand this is a expensive job.

There is no manual fix. If you are driving a Cadillac you will need to pay to have it replaced.
1 more answer
take off air door actuator and you can turn the 3" plactic wheel that the actuator turns.Just gently take off plastic in front of drivers side in front of knees and take out 3- 2.5 mm screws on actuator,then wiggle it off of shaft of the 3 " wheel.It is the actuator closest to the radio.Check out other websites on how to change air mode or air blend door actuator.This is job any halfa-- mechanic want=to=be can do.Cadillac dealer was the only one in the world that had my actuator replacement.