Try rebooting the machine first.
1. Go to Settings.
2. Choose
Network.
3. Select your Network name.
4. Press the
Play/Pause on the remote, and then follow the steps.
If you can not find your Network, try to check if the
Wi-Fi is on.
If the above method does not work
1. Select
Settings on the Fire TV cube.
2. Choose Network.
3. Select your Network.
4. Press the Menu button.
5. Press the Select button to forget the network.
6. Restart your router.