Before continuing. please make sure to run through this on a TEST SYSTEM before committing to live.
Do a cashbook data import. For this, import transactions from System Admin - Data Imports and this would deal with the open Cashbook transactions.
Raise a 1 sided journal through the bank to bring the bank into line with the nominal control
Code the analysis back through the bank. It will be a contra entry so the nominal control doesn't move, but raises a transaction through the bank.
Perform a dummy cash book rec to match that transaction off.