Please use spoiler flag next time, your post was visible in the homepage.

Please read this: https://docs.codewars.com/training/troubleshooting/#post-discourse

And this:

The number can be negative already, in which case no change is required.

Your function returns a positive number when the input is already negative. The function's name doesn't match either, see the initial code:

function makeNegative(num) {
  ...