3296 trimpot adjustment
You can't define an increment or decrement of the resistance, all that you do by turning the trimmer screw is move the wiper toward one or the other end.
Depending on the way the trimmer is wired the rotation direction can have a specific meaning.

The direction of the wiper movement is already shown in the graph you have provided, turning the screw clockwise moves the wiper (pin 2) towards the end named 3 and turning it counterclockwise moves it towards the end named 1.