Currently, the functionality to close an account (including Crypto accounts) on your Trade profile is only available via the Trade mobile app.

Please empty your account to bring it to a $0 balance before closing your Crypto account. 

While logged in via the app, select "Accounts" from the menu, then "Manage accounts". Select your Crypto account from your list of opened accounts, scroll to the bottom, and you should see a "Close this account" prompt. This will bring up a confirmation screen for you to confirm if you'd like to close your account.