Generally a not guilty plea can be entered by mail on civil traffic offenses. Call the court clerk and ask about their local procedures for adjourning (or rescheduling) the initial appearance or for entry of a not guilty plea by writing. This page provides a very basic example "not guilty notice" form for the Madison Municipal Court:
Check with your local office of the court clerk
This is not intended to be legal advise or as legal representation. I am a California personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters.