There are a couple of options:
1. Search your emails for an email from Guild (guild.co) e.g. welcome email, group digest email. Wherever those emails are being sent is the email address you used to register.
2. If you cannot find any emails from Guild, get in touch with support letting us know your name the email address you think you used. We can check our records for your details.
Find out more about what to do if you're not receiving emails from Guild.