If you have an Activation Key it can be passed to the installation script and activation will be completed on your behalf as part of the install.
Create a file for the Activation Key e.g.
activation_key.txt and paste in the Activation Key you received in you confirmation email.
When running the install.sh use the parameter
-a or --activation-key-file so your command might look something like this
sudo bash kasm_release/install.sh -a activation_key.txt.
This will not work with an offline air-gapped install, as Kasm Workspaces must contact an activation server to complete licensing your installation.
In a multi server install this option only applies to the database role.