Hello@@User17532856358633354650
Welcome to the LastPass Community.
To change your master password you need to log into your LastPass vault, go to account settings and from there you will be able to do it.
Now, if you do not know your master password you may recover it by following the steps outlined on the link below:
https://support.lastpass.com/s/document-item?bundleId=lastpass&topicId=LastPass/recover-master-password.html&_LANG=enus
Please let us know if there is something else we can do for you.
Greetings!
Heyner | Customer Care
Thank you.