DNS not correct work

DNS changes take time. Please allow 72 hours for your DNS changes to be reflected everywhere. Also, please share a domain.

However, if you cannot add your domain after 72 hours:
Unfortunately, it seems like the register.it service does not work with services where you must point the nameservers to verify your ownership. If the domain you purchased is not of the .it ccTLD, you can transfer it to another registrar.