If the light on your accessory is flashing, you need to update your accessory's firmware. Follow these steps:
In the accessory screen, select the accessory:
Tap "Edit Accessory"
Scroll down and select "Update" in the Firmware update section
Your accessory will begin downloading the firmware, the download progress will be shown. DO NOT power off the accessory at this time.
The "Firmware Update Successful" notification will appear after the firmware update is completed.