The number of units and items you can see in the pop-up window after completing the Tournament has already been multiplied. You will receive the same information in the in-game message from Lord Oberon.
Your reward surely has been multiplied if you meet the following conditions:
1. You must be a fully-fledged member of your League. For this purpose, you have to complete the 7-day trial period in your current League, be on the main squad for more than half of the Tournament duration, and have a rank higher than Neophyte.
2. You must collect a minimal required number of Points according to the Tournament conditions.
The reward will not be multiplied in the following cases:
1. If you abandon your League before claiming the reward, including cases when you join it again shortly after leaving, the reward for this Tournament will not be multiplied.
2. Players with the rank of Neophyte are not considered fully fledged League members; therefore, their rewards for Tournaments will not be multiplied.