A quick look on the internet revealed that you can't change the Echo / dot's name, but you can change the call sign or watch word.
Here are the available options and how to change it.
original
https://www.howtogeek.com/249342/how-to-change-the-amazon-echos-wake-word/
Home, Settings, Alexa Devices, "Wake Word"
or from the app
- Tap the Alexa icon to begin.
- On the Home screen, tap the “hamburger menu” icon in the upper left-hand corner of the app’s screen.
- Tap “Settings” from the menu that appears.
- On the Settings screen, tap the device you wish to change the wake word on.
- On the next screen, scroll down until You find the “Wake Word” menu option. Tap it.
- Tap the pull-down menu to display the available wake words for your device. At the time of this article, the available choices are Alexa, Amazon, Echo, and Computer.
- Tap the “SAVE” button to save your selection.
- The app will tell you when your changes have been saved.
- Use your new wake word to wake up Alexa on your Amazon device.
Options for name include Alexa, Computer, Amazon, Echo and Computer.