There are two possible scenarios, in both cases you need to create a GL Code (if you want money in this cash book to be displayed separately in the balance sheet), and also a cash book, and assign a GL Code to this cash book.

Scenario 1: CASH TAKEN FROM ANOTHER BANK OR CASH DEPOSIT

After creating the new cash book, simply transfer money from another cash book that correspond to the other bank account.

Scenario 2: CAPITAL INJECTION

Create a receipt under FINANCE -> RECEIPT VOUCHER. Select the cash book, and another GL Code (could be capital, equity, directorABC etc.).