I don't believe it's about having the game or not. The thing is the account. You need to create an account using the Play For Free button on GameHag. Otherwise, your tasks are moer than likely to be rejected
in 3 steps
Choose the game that interests you and play itfor free.
Every game has some quests for which you will receive Soul Gems.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
You know that on Gamehag you can get real rewards for free, right? Join us, complete walkthrough and get your chest!
Did anyone had war thunder already before you knew about Gamehag? And is it possible to delete then reinstall the game and earn rewards?