On the Dashboard scroll to your account balances and tap on the Savings row to expand it
Tap on your Smart Savings account, which will be right below your bank account's savings accounts
Select Options in the upper right corner
Tap on Edit Savings Plan
Select Close this account and then confirm you wish to close the account.
There are a few reasons why you might be unable to close a Smart Savings account
You have have a Smart Savings tranfsers that's being processed. You'll be able to close your account as soon as your transaction settles and is available, which can take up to 3-4 business days.
The checking account that your Smart Savings account was connected to has been closed. If this is the case, please message support requesting a "Smart Savings account change" to add a different checking account to send your funds to.