Hello
With Ubuntu 120 we do like this to add a repo.
deb [arch=amd64] Index of /repo/6.4/ubuntu /bionic multiverse
How do we do with Zorin Snap
I did manually edit my sources.list
Sorry not sure I understand your post but with the latest Zorin you are on Ubuntu 20.04LTS, and if you want to install the Fortinet Client then these commands in Terminal should do it:
Ubuntu 18.04 LTS and 20.04 LTS
Install gpg key
wget -O - https://repo.fortinet.com/repo/6.4/ubuntu/DEB-GPG-KEY | sudo apt-key add -
Add the following line in /etc/apt/sources.list (You'll need to open this as Root I believe)
deb [arch=amd64] Index of /repo/6.4/ubuntu /bionic multiverse
Update package lists
sudo apt-get update
Install FortiClient
sudo apt install forticlient