You can certainly try to work out a deal with the plaintiff’s attorney representing the judgment creditor. If you have access to a lump sum of cash, you may be able to settle for less than 100 cents on the dollar. However, unless you have cash, there is not much incentive for the plaintiff’s attorney to cancel the garnishment voluntarily.
You could also file a lawsuit in the county where the fi fa was issued to “collaterally attack” the judgment. A collateral attack is one where you argue that the judgment should be voided because you were not properly served or because there is some other fundamental defect in the lawsuit process.
Usually, state court judges will not allow you to argue the merits of whether you actually owe the money if you did not respond in time. For example, if you were properly served a lawsuit to collect a debt that was not yours, but you failed to answer the lawsuit and a judgment was issued, most state court judges will say that you cannot collaterally attack the judgment. This is why, by the way, that you should never ignore any type of lawsuit.