First, do you have a switch online subscription? You’ll need that.
Then if you go to the top post of this thread there is the lobby code to access the DiS tournament in the friends doc. You’ll need to go to the online menu in MK, then select tournament and enter this.
Also worth noting is that occasionally a thing happens where you leave and go back to find nobody else in the lobby. The workaround we’ve found for this is to instead of going to the tournament option, go to the option st the top that says something like friends & rivals and just select one of us who you have just been racing again and that should put you back in there with us.
Pretty glad you asked as I’ve mostly written the op for the new thread now 