Unlinking any account from a given bank will unlink all accounts from that bank. However, you can hide any of your linked bank accounts to remove them from calculations (like "How this month compares" or "Top categories") by following these steps:
In the NerdWallet mobile app:
Log into your NerdWallet account.
From the HOME tab, tap on the account you want to hide from calculations.
Scroll down and tap on the slider next to the option you want:
Hide from Net Worth only OR
Hide from calculations