For someone the firm has invited to send it a matter it has not taken on. You are not a client yet and this is not an engagement — the firm may decline, and will tell you if it does. You reach what you send and your own details; nothing else here is open to you. A password is all you need: no authenticator app, and nothing to set up beyond choosing that password.
Forgotten your password? Reset it by email — you will still need your authenticator to choose the new one.
A second factor is required on every account. If you have lost your authenticator, email jhenry@jhenrylaw.com — it cannot be reset from this page, and resetting a password will not get you past it.
Set a password from an invitation but never got the email asking you to confirm your address? Resend it.