The link will redirect you to Apple where you enter your Apple ID and password.*
You then will need to select permissions for ChannelMix to have on your account. You only need to select Account Read Only.
Once you have completed the OAuth process and returned to ChannelMix, save your connection and connect it to the desired ChannelMix profile. You will then need to select the appropriate Organization ID from the populated list to associate it with the profile in the connection.
*You will need to have the user's personal Apple ID associated with the organization account.