Quote:sorry, I still don't get it
I have
QE QD XFB OFEJ CWO YBQGQULNL EX ABLCEPL UQML QWEX C WLH CNL XM LWUQNPELWVLWE
no idea how to find out what stands for what
As Kiwiana explained, you have to scramble the alphabet starting with Carol, to get the alphabet as it was used in the scrambled message.
So you know that a C in your scrambled message stands for an A in your decoded message. A = B, R = C, O = D, L = E
Then you have two ways to possibly continue. M, because it is the next letter after M, so M = F, N = G and so on.
Or with B because it is the next letter of the alphabet you don´t have in the key, so, B = F, D = G (skip C because it is already in the key).
The easiest way of trying here is with the word "OFEJ" because you don´t have to write out the whole alphabet to see which of the two options is the correct one.
Spoiler (highlight to make visible):
OFEJ (second option) = DIHM - obviously false because it is still gibberish
OFEJ (first option) = DUTY