Yes, you can delete it. You will need to screenshot or link this GA in your ticket because I cannot leave a comment on the GA.

Hey there, i'm here about a message a receive from you following this giveaway https://www.steamgifts.com/giveaway/72Svw/coins-battle
I'm afraid i'm no longer in those groups to view the giveaway so i can't reply on that behalf but if you want to delete it i agree to do it in that case