I understand you want to sign in to your Fire TV Stick using Amazon MyTV by entering a registration code.
When you choose the sign-in option on your Fire TV Stick, the device may display a registration code instead of asking you to type your login details on the TV. This code is used to securely link your Fire TV Stick to your Amazon account.
Turn on your TV and open the Fire TV Stick setup or sign-in screen.
Select the option that says Sign in using a code or Register on the Amazon website.
A registration code will appear on your TV screen. Keep this screen open.
On your phone or computer, open a web browser.
Visit the Amazon MyTV registration page shown on your TV.
Sign in to your Amazon account when prompted.
Enter the registration code exactly as it appears on the TV screen and submit it.
After the code is accepted, your Fire TV Stick will automatically finish signing in.
The home screen will load, and you’ll be able to access Prime Video and other apps.
Important:
Make sure you’re signed in with the correct Amazon account before entering the registration code. The account used during this step becomes permanently linked to your Fire TV Stick unless you deregister it later.