How do I send the game to the winner?

Post a message on one of their giveaways if they’re not responding to your friend request. If they still don’t respond or you can’t contact them you can always reroll after a week.

just like damianea said, the easiest way is to leave a message on one of their own giveaways. explain whats going on and try adding them as friend on steam.

i believe as gifter you are also able to send them an email. try that if they dont answer or they dont have any giveaways of their own.

if everything fails, after a week has passed youre able to reroll the winner

First of all, if you are going to give a gift via steam, add me as a friend to the description of the gift you will give, and you should leave a description such as I will send the game via steam. (Users don't usually read, but it's always important to write a description anyway.) Look at the steamgifts profiles of the winners and leave a comment on one of the gifts sent. If they still don't answer in more than 7 days, take screenshots and report it to support. Have a good day.💙

try contact via email and wait 7 days, if no contact reroll

Thanks -- the two remaining winner did respond to my "add friend" request. I will take the advice of velosterz if/when I create another give-away.

For future reference, you can go to the giveaway's page, click Winner on the left side, and it'll show you not only the username of the winner but also their email address. Then you can send them an email to get their attention, and let them know you're trying to reach them through Steam to provide their game.