You can close any of your savings accounts from within your App by simply selecting the Account → Close Account. You will need to move any existing funds into your main Everyday account before closing the account and this will have a Notice period associated to it.
​
You can still view the account in your App showing a small padlock during the Notice period, but once the Notice period has passed, the funds will be deposited into your Everyday Account (including any accrued interest, less tax) and the Savings account will no longer be visible in your App.