So, assuming you’re using Bart’s starter kit, and that you have the 6-pin cord that Bart recommends for it, then one PCB plugs into the Jackpot, and the other goes into the pendant. Also assuming you have installed the firmware onto the M5Dial as shown in the wiki…
Then, finally you’ll need to modify your config.YAML file as shown in the wiki, but with a key difference to the GPIO numbers for transmit and receive. I explain the GPIO edits in my build thread here: Fluid Dial (Fluid NC dial pendant by Bart Dring, using M5 Stack's M5 Dial) - #9 by DougJoseph