When was this secondary Skype account created?
In the past, in the early days of Skype, Skype accounts were created using a simple Skype Name, which was just a text, e.g. "name". This Skype Name was the Login ID for this Skype account. However, users were also advice to add a recovery and information email address or a mobile phone number.
Later on, Skype accounts required an email address to be used to create an account. This email address was the only Login ID for this account, but a Skype Name (Skype ID) was also assigned to this account with the form of live:name, where "name" was the name of the email address in front of the "@" sign. This Skype Name was the unique Skype ID, but could not be used as the Login ID. The only Login ID was the email address used when account was created. Another email address or a mobile phone number could also be assigned to this account, but only for the recovery and information purpose.
When Skype was fully incorporated into Microsoft, accounts could only be created using a Microsoft email address or a mobile phone number. A technical Skype Name (Skype ID) was assigned to this account and was in this form - live:.cid.<random letters and numbers>. Again, this Skype ID cannot be used as the Login ID, Instead, the emails address or the mobile number was the only correct Login ID.
After Skype was retired, in order to migrate Skype account to Teams, exactly the same Login ID must be used in Teams. In the case the password was forgotten, users can recover this password using the assigned recovery email address or mobile phone number. If users don-t have access to the recovery email address or phone number, then the Microsoft account recovery form can be used.
https://support.microsoft.com/en-us/account-billing/help-with-the-microsoft-account-recovery-form-b19c02d1-a782-dee6-93c3-dc8113b20c42
Do you have access to a Windows or Mac computer. It would be easier to handle Teams accounts using the online Teams for Web application.
https://teams.live.com/v2/