You just have to change the screen resolution so that your nickname is no longer hidden by the rewards window.
First, click on your avatar (top left), then on the Options tab. Now, change the resolution (1680x1050 worked for me) then click on Yes to save the settings.
Close the window and head to the rewards panel.
To open the rewards panel, from the main screen look to the right, there's a button with 3 bars inside, click it and a the reward panel will appear.
Now just click on Daily login rewards. You have to login for 7 days and claim your rewards there and then take a screenshot to finish the quest.
Here's a sample of how your screenshot should look like (rewards claimed for 4 days only) :