Firstly, restart the Scout pairing mode by connecting a charger, and force close the Find My app and reopen it. Check to see whether the Scout can now be added in the Find My app.
If not, your Scout has probably made an incomplete connection to the Apple Find My network. You will need to perform a factory reset to restore the connection. This will break the bonded/encrypted connection. Remove the Scout from the Knog app first, forget the device from you phones Bluetooth device list and then perform the factory reset.
Do not attempt a factory reset while the Scout is in an armed state