This was covered here
And documented
The player API is documented
From your code you seem to be using the Interactive player and not everywhere, documented:
Check the docs, and check the console of the browser you are testing in for errors.
I took your player code, and called the changeChannel function.
Works fine.
However in your source code you do have two elements with the id of “stream”. One is the div and one is the channel input field. So you fetch the channel name from the input and then try to update that input field to be an existing Twitch Player, which of course doesn’t work