If a user is already registered with tchop, new login credentials or signup link will NOT be generated for that user.
To access the content of your company app, the user simply needs to install your company app and login using the tchop credentials. In case the user do not remember their tchop credentials, simply try resetting the password: Resetting password
However, you can decide if you want to notify the existing users about their invite in the channel. To do so, simply enable ‘Notify existing users’ option at the time of inviting the user