Manually Attaching Twitch Profile
You can manually attach the Twitch profile to the WordPress user by assigning a Twitch username.
If you go to your personal profile page in the WordPress admin panel and scroll down to see a Twitch Data section, you will find connected Twitch profile data and a button to re-connect a new one.
If, as the website administrator, you go to the same place on other user profiles, you will find an option to attach the Twitch profile manually by saving the Twitch username.
If you attach the wrong username, another person can log in with this WordPress account. Also, a new account will be created when the correct person returns.
Here, you'll be able to read more about finding the Twitch username.