Have an iPhone 11 trying to change the name on a Bluetooth device
Instructions for changing name of Bluetooth device on phone not working
Question marked as
The ability to change the name of the device will depend on the device itself. Not all bluetooth devices support name changes.
If following the steps in the link below does not produce an editable Name field, then the device in question simply does not support having its name changed.
See here: Change the name of a Bluetooth accessory - Apple Support