Hello @Diego Alberto Savoldi,
Thanks for sharing your question with the Klaviyo Community!
It sounds like you are talking about the double opt-in confirmation email that comes through when a custom subscribes to your list. You can edit this confirmation email by navigating to Lists & Segments > your list > Subscribe & Preference Pages > Email Confirmation.
I also elaborated further on this in a similar Community post which i’ve attached below with some further resources that may help you:
I hope this helps!
David