If your Bluetooth device still doesn’t connect to your iPhone, it might be time to restore the smartphone’s network settings back to their default. That erases all the data and settings related to VPN connections, cellular and Wi-Fi connections, and Bluetooth devices linked to your iPhone (via Apple). It can also help if your iPhone has no service, even though it should. To perform a network reset, head over to Settings > General, tap on ‘Reset’ and select on ‘Transfer or Reset iPhone.’ On the menu that pops up, tap on ‘Reset Network Settings’ and then enter your passcode to confirm.
This will turn off your iPhone, reset all the network-related settings, and then turn it back on. As a bonus, restarting your iPhone can help fix any underlying memory-related issues, or other software glitches. Once the iPhone has finished restarting, head over to the Bluetooth settings, check if Bluetooth is enabled, and then search for the required device. Usually this will address a Bluetooth issue, though you should only reset your iPhone’s network settings as a last resort, since doing so will also erase all the saved Wi-Fi passwords and Bluetooth devices you’ve ever used.