You must access the channel you want to get the code:
In the channel URL, you will find a code that starts with "UC...".
If you don't find the code that starts with "UC" in the URL, you must access some video from the channel.
And then click on the channel name (where it is highlighted in red). Then you will be redirected to the channel and you will find the code in the URL.
If you still have questions, check out our playlist of tutorials on Youtube.