javascript add number to random array

Question

I need to add any number to random array to the preset position and and move elements after him. I just wrote code for random array how to continue?

var CreateArray = (...lengths) => lengths.map(length => (
  Array.from({
    length
  }, () => Math.floor(Math.random() * 3000000))
));
var randomarrays = (arrs) => {
  arrs.forEach(arr => {
    randomarray(arr);

  });
};