I remembered to explore Battle Record of the Arena this morning, located at botton right of the page.
So if you click it, you will see a list of players that you have attacked, and the ones that have attacked your team, and whether the attack is Victory or Defeat.
Click on individual player to see the battle reports. Example as below. There are four rounds, so that's why we have to appoint 4 heroes.
If we click the Data Statistics, this will tell you how you have been doing in the Arena.
So, until I have better teams to further go up the ranks😎😎