Apple TV+ family share

When in a Family Sharing group, then each group member signs in using their own Apple ID account.

Add additional Apple ID accounts to the Apple TV app - Apple Support

* Select the user profile at the top of the sidebar, then select Add New User.

or

* Select Settings, select Accounts, then select Add New Account.

Ok. This time in smaller steps:

1. Verify that your smart TV has the Apple TV app. Launch the app.
2. Navigate up to the Home icon in the upper left corner, so that the sidebar expands.
3. Navigate up to the (currently active) user listed at the top. Click it. A pop-up window should show the registered user(s) and an option to add a new user account.
4. This users listing is also where you can later switch between active users.

or:

1. Verify that your smart TV has the Apple TV app. Launch the app.
2. Navigate up to the Home icon in the upper left corner, so that the sidebar expands.
3. Navigate down to Settings. Then navigate to Accounts. Then navigate to Add New Account.
4. For switching between accounts, see #4 above.

Good luck!