If you signed up to Covve with email and password, your Covve username is the email you used to sign up. 

If you signed up with Google, your username will be the e-mail associated with your Google account. 

If you signed up with Apple, your username will either be the email associated with your Apple account, or, if you chose to hide your email from Covve, it will be an anonymous email provided by Apple.

You can check your username by opening the Covve app, tap the gear icon (top left) -> General -> Account