1. On the official Ubuntu dependency library website, search the QEMU Guest Agent with Ubuntu 16.04, and download the offline deb package of QEMU Guest Agent at version 2.5.

    https://ubuntu.pkgs.org/16.04/ubuntu-universe-amd64/qemu-guest-agent_2.5+dfsg-5ubuntu10_amd64.deb.html

  2. Install this offline deb package.
    dpkg -i <package.deb>    //<package.deb> represents the offline deb package of QEMU Guest Agent at version 2.5.
  3. Modify the password on the UI. If no errors are reported, the modification is completed.