For both Android and Apple iOS you can download the "Rocket Chat" app in their associated App Store.
When When downloaded, installed and started on your device, select "connect to server"
Workspace URL: chat.cept.org
User credentials:
Email or username
Password
You will find the chat username and password on your CEPT user profile page, near the bottom:
https://www.cept.org/ecc/start-page/profile/
...
It is possible to change the password directly on the Chat system by either using "Forgot password" on the login form, or in the profile settings on the chat system.
Please note - by changing the password directly in the chat system, this will invalidate the password shown at the profile settings on the CEPT portal.