Work through these checks in order
Charge it and put it into the correct pairing mode.
Turn the phone/computer and accessory off and on before retrying.
Forget the accessory on the device and remove old host connections from the accessory if supported.
Move away from many active Bluetooth devices and keep the accessory close during pairing.
Confirm that the accessory supports the device and the feature you are trying to use.
Before an erase, restore or repair decision
Confirm what data is backed up, what a reset or restore will remove, and whether you still need access to account credentials or authentication methods stored on the device.
When professional service makes sense
Hardware damage, repeated power failure, liquid exposure, battery swelling, damaged ports, broken displays and problems that persist after low-risk software checks can require qualified inspection.