Once you have filed for bankruptcy, you will need to give the court a list of all your creditors and their addresses. The court will then notify all of your creditors about your bankruptcy filing. Once the creditors have received notice, they are required to take the steps to suspend the garnishment.
If you are under any time constraints, you may want to have your bankruptcy attorney forward the filing directly to the creditor. This is a faster and more direct way to communicate this information if the wage garnishment is scheduled to begin soon.