If you still can't pair or connect the Bluetooth accessory To find out if the accessory is compatible with your iOS device or iPad OS, contact the accessory manufacturer. The easiest way to fix most Bluetooth problems on your iPhone or iPad is to turn Bluetooth off and on again. This is particularly effective if your device is having difficulty pairing with a Bluetooth accessory. It will also help if you accidentally turned off Bluetooth on your device.
If you've tried all of these options and you still can't connect an accessory to your iPhone's Bluetooth, it's probably time to contact Apple Support.