Login to the idol champ app (for the tutorial, see here)
To vote, click on the “vote” with the heart tab at the bottom of the screen of the screen as shown and scroll down until you find the Show Champion logo and click on it.
Click on the heart next to Dreamcatcher’s Scream. You can vote a maximum of 3 times per day per device. A yellow notification at the bottom of the screen will show you how many votes you have left. After voting 3 times you will see the voting % and this popup below.