After successfully connecting to your Bank, use Developer Mode to access the following Menu:

Then, update the Last synchronization date for the account(s) you selected to synch and click Fetch Transactions if your date is prior to the previous date:

If you already have transactions BEFORE the date you want to start in Odoo, you can clear them out of Odoo. 

First, navigate to the Transactions Menu from the Accounting Dashboard, using the Card representing your bank account Journal:

Switch to the List View, select the Transactions you don't need (be sure to filter correctly based on date) then delete them:

Note: depending on the third party provider used to connect to the bank, you may be limited to the past 90 days worth of data.

Alternatively, you can set a LOCK DATE to prevent Odoo from creating entries before your desired date, this approach is explained in https://www.odoo.com/documentation/18.0/applications/finance/accounting/bank/bank_synchronization.html