Go to the courthouse that issued your original restraining order. They will likely have a specific form you need to fill out to extend the order. If you cannot find it or there is not a specific form, ask the clerk of the court. The clerk will be able to either supply you with a form or with a sample motion you can copy.
When you finish, make two copies of the form (or have the clerk do it for you). File the original with the clerk, keep a copy for yourself, and send a copy to the defendant against whom you have the restraining order.
Your submission needs only include the date of the restraining order, the date of the hearing, and a statement that you feel a continuing need for protection. You do not have to be more descriptive than this.
I hope this answers your question. Good luck!