If you have forgot your password, you can use the link
Password lost on the login page.
You need to set the password recovery method first, in the Preferences / General / Password tab. Pick
Seccret question or
Secondary email and save.
If the link or preferences option is not visible, you may need to contact your platform administrator to enable password recovery in SOGo.
SOGoPasswordRecoveryEnabled = YES; in sogo.conf. This option is available since SOGo 5.8.0