how to give a HBKey if the page is already claimed by me?

Just push the "gift" button near the game. It looks like a gift box. On the page you've claimed.

It must be insurgency, I don't think you can gift the shared keys.

why did you claim a gift page of a game that you already own?

Did you redeem a gift copy of Insurgency on your own acount?

If you log out of Humble and look at the page it should show nothing where it shows who the link will redeem to. Give the link to your friend. It should redeem to the person who is logged into Humble.

If your friend gave you a single game from a bundle and you claimed it, you can't gift it. It must be redeemed to your account. Alternatively, you could get another person to log into their steam account and redeem it onto that account, but you can't get a new gift url to hand out.