1.1 On the Publish a Service Tunnel doc, navigate from Steps to Publish a Service Tunnel > Step 1: Create a Tunnel Policy to create an access policy. This access policy determines which of your end users can access your Service Tunnel.
1.2 Is SCIM enabled in your org?
If yes, then directly assign users to your Tunnel policy.
If not, then instruct end users to log into the CSE app and register their devices; Afterward, assign your end users to the Service Tunnel policy.
2.2 Configure a SaaS app (via allowing IPs) in your Service Tunnel configuration: On the Publish a Service Tunnel doc (linked above in Step 2.1), navigate to Network Settings and see Step 2.4 for how to configure a SaaS app.