I need help, I would like to dim LEDS of an Christmas  tree with potentiometer.
Here is my electric diagram (Please note I'm a beginner in electronic)
[![enter image description here][1]][1]
I don't know how to choose the good value of the potentiometer. Does my diagram is correct?
I noticed that by adding a resistance in series on the postive side of the out powering cable I manage to lower the brightness of the tree, the goal of the project is to be able to adjust the brightness with the potentiometer.
Here is a picture of the power supply.
[![enter image description here][2]][2]


The Christmas tree
[![enter image description here][3]][3]


  [1]: https://i.sstatic.net/esJZd.jpg
  [2]: https://i.sstatic.net/7HauS.jpg
  [3]: https://i.sstatic.net/vFYyS.jpg