Download the ".s9pk" and side-load it in StartOS under "System -> Sideload a service". Then configure the cloudflare service on your server (it just needs your CF tunnel API key) and start it.
The key can be found here:

(use the copy button, paste the full command in notepad, and then copy just the full key)
Then you can use the Cloudflare Zero Trust Tunnels dashboard to setup "public hostname" routes, like this:

