I'll help you add the new account and provide details about merging them. For adding the new account, you can follow these few easy steps:
Go to Accounting > Chart of Accounts.
Click the New button and add the new account details.
Select Save and Close.
Please see this sample screenshot for a visual reference:
Once added, you can merge it to the other account. Important: Merging accounts is permanent. You can't undo this later on. QuickBooks uses some accounts as the default for certain features. These, like accounts connected to online banking, can't be merged or deleted.