Manually updating VR Tourviewer for Gear VR with the use of APK files is discontinued.
VR Tourviewer is now only available in the Oculus Library. To get access to VR Tourviewer from the Oculus Library you can use an Oculus Redeem Code.
You can get your Redeem Code here.
After entering the Redeem Code in your Oculus account, the app will be available in the Oculus Library on your VR device.
Make sure to make a backup of the tours stored on your device, and then uninstall your manually installed version before adding the app in your Oculus Library.
Note that the app is then available from the Oculus Library in VR, instead of the Android launch screen.