A solid red light from the LED generally indicates the device is in what’s called a “bootloader state.” This is a state where the trainer will not be responsive or able to be detected or controlled by virtual software. A remedy for this is available through the Saris Utility app for iOS and Android.
NOTE: for Android users, please make sure Dark Mode is disabled while performing the update, as the progress bar can be hidden or difficult to see in Dark Mode.
If you haven't already, download the Saris Utility app (iOS/Android) from your respective app store. Once installed, select Settings at the bottom of the screen, and then tap the Sensors dropdown. This will initiate a Bluetooth scan (make sure Bluetooth is enabled on the device), and “Saris_Boot_xxxx_xxxx” should show up on the list of Sensors. Swipe left on this listing and select Set Current, then tap Firmware at the bottom of the screen. Once on the Firmware screen, select the latest version (top of the list), and tap Install. This update will essentially overwrite the existing faulty software on the trainer, ultimately instating a proper and fully functional software version and restoring the trainer to a working state.
A walkthrough can be found here: https://www.saris.com/pages/firmware-saris-utility-app