Is this the first person setting up the chat, or are you joining using a Setup Code from the other person?
Read or send this to the other person over a secure channel (in person, a phone call) — not plain email or SMS. They'll enter it during their own setup. This code is the master key to your chat; anyone with it can read every message.
Next, save your personal Recovery Key. If you ever forget your password, this is the only way back into your message history.
Paste the Setup Code the other person shared with you.
Now save your own personal Recovery Key — needed only if you forget your password.
Your login password was reset. Enter your Recovery Key to unlock your message history, and choose a new password.