You check out if you want viber by visiting their website.
Installing could not be easier.
Install it first on your mobile (ios or android) – see that you have an account.
Then proceed to ArcoLinux and install with
yay -S viber
You will get popups guiding you through the installation. You scan a code with your phone and that makes the link to your ArcoLinux desktop app.
Then you will be able to receive and send information from your desktop.