To address the issue of the Wahoo Fitness app crashing and your inability to use the KICKR, follow these steps:

1. Reboot Your Device
- Start by restarting the device on which you have the Wahoo Fitness app installed. This simple step often resolves minor software glitches that may cause apps to crash.

2. Reinstall the Wahoo Fitness App
- If rebooting does not resolve the issue, uninstall the Wahoo Fitness app completely by going to your app settings. Once uninstalled, reboot your device again.
- After the reboot, download the Wahoo Fitness app from the App Store (for iOS) or Google Play Store (for Android) and install it anew. This can help clear any corrupted files associated with the app - learn more.

3. Check for Device Compatibility and Updates
- Ensure that your smartphone’s operating system is the latest version available. An outdated OS can conflict with app updates or functionalities.
- Confirm that the Wahoo Fitness app is also updated to the latest version to incorporate improvements and fixes.

4. Reset Your KICKR
- Unplug the KICKR from the power source for about 30 seconds. This resets the trainer and may help in establishing a stable connection afterward.
- Power it back on and try launching the Wahoo Fitness app again - learn more.

5. Clear Bluetooth Connections
- Close all other apps running on your device to avoid conflicts with Bluetooth connectivity.
- Ensure that no other devices are trying to connect to the KICKR. Go to your Bluetooth settings, and if any previous connections are listed, remove them.
- Reconnect your KICKR to the Wahoo Fitness app by starting the app and following the prompts to pair the device.

6. Check GPS Settings (if applicable)
- For some users, GPS settings have defaulted back to "off," causing connectivity issues. Verify that GPS is enabled in your device settings which may help in occasional app crashes - learn more.

7. Contact Wahoo Support
- If none of the above solutions work, it may be best to contact Wahoo Fitness support directly for further assistance. They can provide more troubleshooting steps specific to your device or account issues - learn more.

By following these steps, you should be able to resolve the crashing issue with the Wahoo Fitness app and successfully connect to your KICKR.