Awaiting feedback from one week

create a support ticket. if you have given a key, the support can check if they have seen it so they can mark it as received or reroll the ga. if you have send a giftlink to the mail, they might just mark it as received and if you have send a gift, they might reroll it

If the winner hasn't seen the key, ask support for "Request New Winner".
If the winner has seen the key ask support for "Request Received Feedback"

I suggest you to contact the winner to ask them to redeem the key and leave feedback. If they do not answer in a while, contact support as other users said.

faq:

What should I do if the winner of my giveaway has not redeemed their gift, and I'm unable to get into contact with them?
If you contacted the winner of your giveaway on email and Steam over one week ago and they have not yet responded or redeemed any keys or gifts you attempted to send, please contact support to request a new winner. When creating a ticket, we ask you to include data that suggests you made an adequate attempt to contact the winner, such as screenshots of emails, friend requests, or gifts pending on Steam. If the request is approved, a new winner will be generated by the site.