Once your income decreases, you file a motion to decrease everything else accordingly. Your job loss is due to plant closure, not because you are deliberately under-employing yourself.
It is a material change of circumstance. You do your best to find as job a job as you can in the mean time as you will be stuck paying the larger sum until a) the ex agrees to reduce c/s and likely s/s (sorry, but I have to LOL to that. I know it is the reasonable thing for your ex to do, but yeah, we all know that isn't going to happen) or b) you get a court order for a reduced amount.
Even if you get a decent job, but still doesn't pay what you used to make, be prepared for the courts to order an imputed income higher than what you actually make. You can argue to make X, and provide evidence to reflect it, but the courts still have leeway to impute another amount.
If your ex was a reasonable person, you could try to mediate this. I'd give her offers to settle based off of your new income, once the new income is in place.
