You don't usually need to. We tidy up inactive accounts automatically, so there's nothing for you to do.
If you'd rather close it yourself:
Tap your USD, GBP, or EUR account
Tap [...] in the top right
Tap [Close account] and follow the steps
Not using it right now? You can leave it as is and come back anytime. If it's closed and you want it back, you'll just need to apply again.
