It's easy. You can update your E-911 registered address on your phone or online in your account at MyMobile. You will want to keep your E-911 address up-to-date on each phone as it is used by emergency services to determine your location when using Wi-Fi Calling.
1. Sign in to MyMobile
2. Tap My account at the bottom of the screen
3. Tap E-911 address
4. Select a line from the drop-down
5. Tap next to E-911 address and enter the new address. This address should be the primary place where you use the line. You must provide a street address. P.O. Boxes are not accepted.
6. Check Make this the E-911 address for all lines, if applicable
7. Tap Update
8. Confirm your address, then click Yes, this is my address
Repeat these steps for any other lines that need to be updated.