If you have forgotten your login account details, you can search in your email inbox to find the account creation notification.
Your login details includes the
Authentication provider - this could be
Salesforce Production/Developer,
Salesforce Sandbox,
LinkedIn, or
Google
Your username - this may or may not be your email address.
You should have this information in an email like this when you created the account.
You can use this information to log into the Gearset app at https://app.gearset.com/.