hello

Hello swathik4317, Mostly your username will be the same as your email Id. you can check your email contents for mails from noreply@appian.community   

You will find your User name and your community edition site url.

or you can send an email to community@appian.com 

Please don't post personal details here, even if just an (unredacted) email address - nobody who uses this forum will be able to do anything helpful with that.  As is mentioned in the Community Edition Guidelines, their direct help email is CommunityEdition@appian.com - where you can inquire about such issues.