Hello,
Multi-factor authentication is a prerequisite to utilizing the Trusted Device functionality of LastPass.
You can find instructions on the Trusted Device functionality here: https://support.lastpass.com/s/document-item?bundleId=lastpass&topicId=LastPass/Manage_Trusted_Devices_for_2FA.html&_LANG=enus
The instructions to enable multi-factor authentication can be found here: https://support.lastpass.com/s/document-item?bundleId=lastpass&topicId=LastPass/enable-mfa.html&_LANG=enus