Fetch the installation package from the Citrix webpage (use „Debian Full Packages“ usually x86_64):
https://www.citrix.com/downloads/citrix-receiver/linux/receiver-for-linux-latest.html

$ sudo dpkg -i icaclient_13.9.1.6_amd64.deb

The Citrix receiver does not search for CA root certificates. Without those certificates you probably get an error which prevents you from logging in. Just run:

$ sudo ln -s /usr/share/ca-certificates/mozilla/* /opt/Citrix/ICAClient/keystore/cacerts/