Since there are no error messages on the device, the technician should check if the battery is sufficiently charged1 If the battery is low, the device may not have enough power to complete the update2 In this scenario, the technician has already determined that there are no error messages on the device. The next best step would be to check if the battery is sufficiently charged. If the battery is low, it could be preventing the device from completing the update process.
Verifying that third-party applications are disabled, determining if the device has adequate storage available, and confirming a strong internet connection are all important steps in troubleshooting issues with mobile devices. However, since the problem in this scenario is related to a failed OS update, it is important to first check the battery level before proceeding with further troubleshooting steps.