It's in the upper right corner of the screen. Then you have to re-enter the new password. Please be careful, you need to enter it exactly as you did the first time. Or else, you have to reset the password.
Open the Phone app .Tap More options Settings. Voicemail.Turn on Voicemail transcription.

* Euro falls to six-week low vs dollar * Japan's yen falls versus dollar, euro * British pound down sharply (Adds new comment, updates prices) By Gertrude Chavez-Dreyfuss NEW YORK, Sept 28 (Reuters) - The U.S. dollar surged to its highest in more than 10 months on Tuesday, tracking the rise in Treasury yields, as investors looked ahead to the Federal Reserve possibly reducing asset purchases in November and an interest rate hike likely to follow. On Tuesday, benchmark 10-year Treasury yields hit a three-month peak, and were last up four basis points at 1.5253%. The rise in yields accelerated after the U.S. central bank turned hawkish at last week's monetary policy meeting, reinforcing the market view for a sooner-than-expected Fed taper.
You could also record a custom greeting in a visual voicemail app, if you have one installed.