And then you can tap on the "Enter a new voicemail password" option, the popup numeric keypad will appear on your screen, then you can tap in a new voicemail password. It must contain 4-7 digits.
Enter a name for the new greeting and then tap Save. Change your greeting. To use a greeting that you've already recorded or switch back to the default greeting: On your iPhone or iPad, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting.

After setting the number on your voicemail, you must also record a personal voicemail greeting. Follow the steps below. Start the Phone app. if you don’t see the numeric keypad, tap “Keypad” at the bottom of the screen. Tap and hold the “1” for about two seconds until the phone automatically calls voicemail. Immediately tap “3” to access voicemail settings. Listen to the options. On most voicemail systems, tap “2” to start the process to record a new greeting. The current personal greeting will play; then tap “2” again to record a new greeting. Say the greeting you want, and tap “#” when you’re done. To save the greeting, tap “1.” The personal voicemail greeting has been set. Hangup the phone. How to setup voicemail using a Visual Voicemail Applications
You can set or change your PIN for your voicemail box if desired Toggle to play the voicemail message date on or off as desired Decide if you want to receive an email and/or sms notification when you receive a new voicemail message.