How to wire Bathroom fan with timer?
You probably should use an English manual
https://blaubergventilatoren.de/en/product/aero-still-100#downloads

The diagram here shows how to connect from the L/N lines of the main panel to the 3 wires (L, LT, N). The second diagram is sharing a light on the same switch.
The S is a manual switch that is part of the circuit. If you do not want a manual switch, then they have a diagram further down to connect just the L and N and use the pull cord.
The way this device works is when you flip the switch to &quot;off&quot;, it keeps running for 2 to 30 minutes after it is &quot;off&quot;. Obviously, if all you have is L and N, then it won't have power, so the L wire is split into L and LT. Your light switch connects to LT and it tells the fan to &quot;turn on&quot; or &quot;start turn off timer&quot;, while it runs off the normal L and N lines.
Beyond that, if you don't know how to split a line, then this installation is beyond your ability and you need to hire an electrician.
Note: The likelihood of your existing wiring having the 2nd live wire is next to none. In your original setup, it would only need one live from the main panel to the switch, and one live from the switch to the fan. This setup requires two live wires; one directly from main panel to the fan and one from the main to switch, then to the fan. There's no reason for anyone to wire it like that with a normal switch, so your new fan probably won't work with a switch. You may have to go with the L/N connection in Figure 13.