JSFiddle - React, Tailwind, and code Playground

JavaScript

function PermutationStep(num) { 
    var sorted = num.toString().split("").sort(function(a,b){return a-b});
    var biggest = sorted.pop();
    sorted.splice(2,0,biggest); 
    return sorted;
}
console.log(PermutationStep(11121));
//console.log(PermutationStep(41352));
//console.log(PermutationStep(999));