How to fix your iPhone 7 Plus that cannot pair or connect to a Bluetooth device after updating to iOS 11.3

Changes to iOS features and services are made once the update is installed. Some features and services may behave badly as a result of these modifications. And this could be why your iPhone's Bluetooth capability isn't working. Restarting the phone's Bluetooth capability may assist to resolve the issue. So, if the preceding approach doesn't work, here's what you should try next:

1. Tap Settings from the Home screen.
2. Bluetooth should be selected.
3. To turn Bluetooth off, toggle the switch.
4. The switch to turn Bluetooth back on after a few seconds. After then, a list of Bluetooth-enabled devices within range will appear.
5. Retry to connect after you've found and selected the Bluetooth device you want to associate with.