What to write in a letter to my landlord to let him know that I am leaving?

Hello,

I agree that might sound really really stupid but I have to write my 7-day notice to my landlord to inform him that I will be quitting the room at the end of this month, but I don't know of to write this in a proper/formal way

Have you got any tips/directions to get me started? I need to post that by today (if possible) and at the moment, I have the blank page syndrome

Thanks in advance.

Regards,
Ludo, feeling dumb to ask this