Close the web browser on the Raspberry Pi if it is still open.
On the Desktop of the Raspberry Pi, we have created an executable script file named start-mit-volume.sh for you. By double-clicking on it, commands are executed to start NodeRED on the Raspberry Pi and load some example flows. After double-clicking, please wait about 5 seconds, then the web browser with the loaded Node-RED frontend should appear.
For your information: You can't do much harm in this environment, clicking on loesche-volume.sh again will restore the original state. Be aware: this process will discard your changes.