You should be able to reset the account without the need for a password.
https://support.lastpass.com/s/document-item?bundleId=lastpass&topicId=LastPass/reset-account-recovery.html
Hello,
Thank you for posting.
For the privacy of the account, we will not ask for the email address. However, if you are certain the account is empty and would like to have the email address available, you can delete the account without the master password. Please, follow the steps in the article:
Once the email address is available to use, you may proceed with the update as needed.
Thank you,
Karol | Customer Care