Manually Attaching Steam Profile
You can manually attach the Steam profile to the WordPress user by assigning a Steam ID.
If you go to your personal profile page in the WordPress admin panel and scroll down to see a Steam Data section, you will find connected Steam 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 Steam profile manually by saving the Steam user ID.
If you attach the wrong ID, 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 Steam user ID.