We have got a new instance. I cant see the option of Retargeting within Web Personalization. I am not sure, is it a separate feature that we need to add on other then Web Personalization?
Attached is the screenshot of Marketo instance.
I'd reach out to your account manager to see if you've purchased this feature. If you have, it's possible that the account hasn't been provisioned properly, but you'd need support and/or your account manager to assist with this.