I cannot find the option of tower of trial, thought i have unlocked it by defeating the boss.... I know it is unlocked but i cannot find the button.... Please anyone tell me where it is....

After tapping the top bar go to the Dispatch tab in the left side.Entering it you will get Tower of trials,merchantry and Hadum Scout.In ToT you can send any other charcters that are above level 45 and to complete all the floors its better to send all other 5 chars if you have created.If you are a newbie I advise you to lvl up your main char upto 60 and do the hadum family quest.Then you can quickly lvl up other chars by grinding them in hadum realm.