I can't activate the final boss of "Ashes of Ariandel"

[plain hearth]

I explored all the dlc "Ashes of Ariandel", but wen i talk to Friede, she say always the same thing and i can't activate the final boss. Can someone tell me if i forgot something or i have to do another thing?

[old cliff]

there's something you interact with in the fly pit

[plain hearth]

oh thank u, now i'm going to see if i found it

[wintry idol]

Did u find it

?

[plain hearth]

yess, i'm trying to defeat them but is really hard

[wintry idol]

Need some help?

[plain hearth]

if u want, why not

[wintry idol]

sadly, im not how for another hour and a half

:

(

[plain hearth]

oh no problem