1. I logged into my account using the "forgot password" setting. Then, a recovery link was sent to the "yopmail account" which can be used to change the password of your account.
2. After changing the password of my account, I also changed my email address, and added a new security question for additional security.
3. Afterwards, I deleted all the forum's messages in the yopmail account so as to prevent the hacker from undoing my change password nor locking my account.
Just quoting for reference. This could be a masterpiece for those who lost their accounts and the hacker used yopmail account.