You won't be using a POT, since the apex will do all the dimming. Since you previous made a fixture with LED's, the only thing new is the dimming cables. Once you're ready to wire the Meanwell's dim+ and dim- to the RJ45, the hardest part is figuring out which wires on the RJ45 are the + or -. Once you splice the RJ45, you'll see a bunch of wires, color coded. The White/blue RJ45 wire goes to the red wire on the meanwell. The green RJ45 goes to the black on the meanwell. Thats your first set. The second one is white/orange RJ to red meanwell, and orange RJ45 to black meanwell. All remaining RJ45 wires are not used. You have 2 RJ45 ports for dimming on the apex for a total of 4 sets of dimmers. You can ask me any questions, feel free to post the questions so everybody can see the answer in case they have the same question.
There's actually a diagram out there on the web which can show you which pins from left to right instead of color coded in case your RJ45 doesn't conform to the regular colors.