You can do this in many ways. But you should use End-to-End encryption to guarantee security. For example, you might use a secret conversation that uses End-to-End encryption on some software like Signal, Telegram and Conversations. Or you can use encryption software like gpg (see https://gnupg.org/) with public key encryption methods, to encrypt the password (or any message), and then you can send it using literally anything, like email or so on.