Attach a Script to the Paddle1 Node.
To adjust the speed the paddle moves at from within the editor
Add an export variable called speed with a value of 500
All the rest of the code lies within the physics_process function.
Add a local variable to determine the movement (direction) of the paddle.
The initial value is zero.
Add "paddle_1_up" and "paddle_1_down" as new Action Commands in the Input Map.
You can choose different command names - no need to stick with mine.
Now check which action command is pressed
and change the movement vector accordingly.
Finally, set the linear velocity of the paddle
move in the correct direction at the speed chosen.
The full code for the Player Paddle is shown below.
Drop a Paddle into your Board Scene
Another way to do this is to instantiate a child scene
Right-Click on the Board node
Position the paddle in the centre of the screen at the left edge.
Test your paddle movement.