Additional Voluntary Contributions (AVCs) – You can pay AVCs either as a percentage of your salary, a fixed monthly amount, or a one-time payment. AVCs are taken directly from your salary.
When you wish to Change/Start/Stop an AVC election, you will be required to fill out an AVC election form. The link to the form is here.
You will need to scroll down to the section entitled: "How do you elect to start additional contributions & what investment options are available". From there you will find the form in the "I Plan" section with further instructions.