Hi @Carrie2 The answer is in the link sent Jonsie sent however to make it easy here is the steps.
You can reset your PIN at any time, just text RESET to 802901. You'll be sent a temporary PIN, which you’ll need to change before you can listen to your messages.
You can change your PIN any time, just:
When you set your PIN, try to choose a number that’s difficult to guess. So don’t go for repeat or consecutive numbers, or the year you were born.