If your tax refund has already been taken you need to request an Offset Refund.
If you think your tax refund may be been taken in the future, you need to request an Offset Refund to protect your tax refund from being taken.
You can request an refund whether your tax refund has been taken from you or not. There is no time limit to make the request, but you should move as soon as you can to protect your IRS Tax Refund.