The rewards won in Tributes are never lost as they are automatically added to your inventory instantaneously.
If you have won the consumables such as a Health Potion, these will be automatically added to inventory which can be found under the “Store” tab. If you have won currency packs (coins or gems), they are automatically credited to your account. You might not have noticed the difference but we assure you that currency is added to your account.If you have won a weapon, armor or other such item, then you can find that in your inventory - use the filter at the top of screen to quickly find it.
If you have won energy then you can use it when you run out of the energy. Just tap on the "Energy bar" located at the top, you will find your extra energy.