How to Rename MacBook
Change the name of your Mac device
Open System Preferences. From the apple menu, scroll to System Preferences and click here.
Click the Sharing folder. Look at the third row at the bottom where it says "Internet & Wireless". To the right of the Bluetooth icon, you'll see a small blue folder with a yellow icon and the word "Sharing" below. Click on it.
Search for current name. At the top of the window that appears, you will see Computer Name : immediately followed by a text field containing the current name.
Change name. You can change that name to any name by deleting and renaming it as you like.
Show MacBook on Finder sidebar
Open Finder Preferences. From the Finder menu , select Finder Preferences. (Customize Finder)
Display MacBook. In the Finder Preferences window, click Sidebar at the top. Look under Devices and look for the MacBook icon (the device has just been named as you like). Click the box next to it and check any other devices or machines you want to appear in the sidebar, then close the window. Your MacBook now appears in the Finder sidebar.