Unlinking a personal account is just like a walk in the park. I'll share the steps to guide you through it.
Go to Banking and select the Banking tab.
Select the tile for the bank account you want to remove.
Click the pencil ✎ icon, then select Edit account info.
Select the Disconnect this account on save checkbox. Note: If QuickBooks is currently downloading new transactions, you won't see this option. Wait a few minutes for the update to finish and try again.