You link a Youtube account via Settings > Accounts > Button: Link account. Then choose Youtube.
First, ensure you have the login credentials for the relevant YouTube account, and log in to www.youtube.com in a separate tab.
Step 1: Navigate to Settings > Accounts > and click '+ Link Account'.
Choose YouTube and specify the roles that are allowed to use the account, then click 'Link YouTube Account'.
Step 2: Now, you need to select the account that has access to your YouTube channel. You can verify this on www.youtube.com. Choose the relevant account and click 'Allow'.
Step 3: Your YouTube account is now linked, and you can confirm this under Accounts. Message indexing may take up to an hour.
Use the following search query source type:youtube AND account:"accountname" NOT user:"accountname" to search via Quick Search for verification and to create your stream.