Update went horribly wrong

As others have written - barely useable because buttons are missing completely. No way to go back a screen. Only sends if I happen to push the right piece of blank space.
How to I roll back to the previous version?
If it makes a difference in your troubleshooting Im using an iphone5s with iOS 8.1.
PLEASE FIX THIS ASAP. Thx.

S.Spencer101 about Google Voice