Reboot the Bluetooth device that needs to be paired and confirm this paired device has Bluetooth enabled. For some devices, you need to manually enter the pairing mode before pairing with the other device. Please refer to the device's user manual for its Bluetooth settings info.
Reboot the phone, then try connecting again: Go to Settings > Bluetooth to confirm whether you can find the Bluetooth device. Click the device to pair it. Some devices will require the users to enter a pairing code to complete the connection. Please follow the pop-up messages to enter the pairing code on both devices.
If the device has been paired but cannot be connected successfully, it is recommended to remove the paired device first and then try pairing again.
Enter Safe Mode on the phone: Please refer to the KB links below for how to enter Safe Mode on the device. If the Bluetooth function can work normally in Safe Mode, the issue may be caused by the certain third-party application on the device. It is recommended that you reboot the phone, backup your personal data and restore your phone (Note: All the data on the device will be erased).