LastPass does not have your master password so they cannot reset it or retrieve it for you. If you are concerned about this, you may consider writing down your master password and storing it in a secure place such as a home safe. If you are already locked out, there may be some options for recovery depending on your LastPass settings. These options can be reviewed here https://helpdesk.lastpass.com/account-recovery/.
If you are unable to access your vault, you will be able to start again with an empty vault. Follow the password recovery method for the services you use to reset individual account passwords. This is usually done with a reset link sent to the email address on file.