If your TV came with the built-in YouTube application, then you may follow these easy steps given below:
Locate and tap on the "YouTube" application to open it
When the app opens, tap on the "Sign In" option
For this, you need to click on the "Gear-like" icon which represents "Settings"
Now, wait until your TV screen displays the activation code
Now, take a mobile phone or open a web browser
From that browser, go to the "youtube.com/activate" page
Now, enter the account login details and tap "Sign In"
After that, you will see a space on your screen
In this field, you need to enter the YouTube activation code
After that, simply tap on the "Allow Access" option
Hurrah! You can start streaming your favorite YouTube shows on your smart TV. If you want to YouTube activate on older versions of the TV then you may follow the same instructions as mentioned above.