To switch from light mode to Wallet's dark mode you have to:
1. Go to your Main Menu
2. Scroll down to where you will see "Dark Mode"
3. Tap the button on in order to enter Wallet's Dark Mode or tap the button off if you want to exit Wallet's Dark Mode.
In order to switch to dark mode on your iOS device, please go to your mobile device's settings.
Settings > Display & Brightness > Appearance: Dark Mode.