We are talking about sync password or sync passphrase? Sync password is your Opera account password, the same that you use to login here in the forums (unless you have created a different account, while sync passphrase is the one that you create to encrypt your synced data.
To reset the sync password, you go to your account login page and click on 'forgot password' (or something like this). To create a new passphrase, you need to reset your synced data and then go to the sync settings to disable passphrase or add a new one.
