I’m assuming you are wondering why the rot13 function doesn’t decode the string.That’s because you have to write the function. It needs to iterate through the string and return a string with all of the letters shifted up 13 characters. Obviously, the later letters like Z can’t go 13 characters higher, you have to loop back to the start of the alphabet. You just have to figure it out. Try writing out the steps then convert each step into code…
That may not be what you need. Best to be clear in the first place