Get adult discus to pair off

I have used quite a few ways to do this over the years. One way is to put six or eight grown or nearly grown discus in a bare bottom tank with a spawning cone at just one end of the tank.
I prefer a 55 long show tanks for this.
If you have mixed males and females the discus will over time decide who loves who and pair off, they will move to the spawning cone and take control of that area in the tank.
Once you see this move the two fish to a their own 20 to 30 gallon tank and let nature take it course.
Another way is to put three fish in a thirty gallon tank with just a single spawning cone. If you have a pair they will soon pair off and make life impossible for the third fish, it becomes odd man or girl out. If you use this method keep your eye on them and remove the third fish before it gets damaged by the matched pair.
They may kill it if you don't.
Another way is to just pick two fish you would like as a pair and put them in a spawning tank and hope your lucky.. You will be right about the sexing 50% of the time. Discus will pair up and spawn with each other and they don't pair bond for life, you can exchange males and females and they will still spawn. It just takes longer for them to re-pair with each other.