On Android Device to change logo or background or music, open the game preview screen.
Step 1: Open the game details / game preview screen.
Step 2: Click / Tap on the setting below preview screen.
Step 3: In Custom Theme Settings Click / Tap on the trash button.
Step 4 : Now you can see a browser or “+” button and it will open a dialogue to choose an image / audio which you want to use.
Step 5: Hit on save button