The name of a Bluetooth, or any other network device, is established when you setup the device, and not all network devices have a mechanism for assigning a the device a name. If your Bluetooth speaker is an Apple HomePod you would have set it up initially following
these instructions. In order to change the name you would first have to reset it following
these instructions then give it the desired new name when you set it up again. If the Bluetooth speaker is a third party device then you are on your own and may not be able to change its name at all.
The name given is K7 and has nothing to do with the name of the product. I don't always remember what K7 i stands for, so that's why I wanted to change it.