Double user account

It seems that I have 2 usernames with the same e-mailadress. How can I changed this or how can I find out the right password of each account

Is this about your forum account or about a account on your Homey?
Homey Cloud or Homey Pro or …

Maybe you signed up with Google/Apple for 1 account, and using your regular email/password for another account

My Athom UN&PW account is perfectly merged with the Google SSO with same email address.
Not sure if that works same for Apple and/or Apple with anonimized-Apple-ID.

Login at a computer and check My Account | Homey for your email address.
or try to login and put a incorrect password for the e-mail address to get te Reset password link.

I Checked the Community forum and see only one account.

Then I’m also not sure if it’s possible.

Maybe you placed a dot (.) between your email address? If you use a Gmail address, the dots get ignored by Gmail so it will end up in your mailbox too.