You can resend the e-mail address confirmation e-mail from the following URL:
https://www.pixiv.net/setting_user.php
E-mail address confirmation e-mail will be sent from "@pixiv.net" domain.
If you have settings that restrict domains on your e-mail account, make sure to allow this domain in advance.
E-mail may be sorted in your spam folder.
Check all your e-mail folders and settings if you don't receive the confirmation e-mail.