We recently discovered a bug affecting users running Android v7.0 or older that was causing the app to crash when trying to complete the most recent firmware upgrade. We released an updated version of the app that solves the issue on May 1, 2020. You can find the update with this bug fix by searching for Embr Wave in the Google Play Store.
If you have any trouble with the app update, an alternative solution would be to upgrade to the latest version of Android. (Here's how to upgrade to Android 10.0)
A third option, if you're not able to do either of those, would be to temporarily install the Embr Wave app on another smartphone or tablet, running iOS or the latest Android version. Open the app on this new device, complete the firmware upgrade, and then go back to your phone, as you should then no longer be prompted to upgrade firmware.