You need to finalize your Chart of Accounts as the first step. Then create/import your List data (customers and vendors). Then you will be able to import transactions (invoices, bills). You will need a 3rd party tool to import certain transaction types (e.g invoice payments, bill payments, sales receipt).

https://transactionpro.grsm.io/qbo

As an additional option, use a backup recovery app for your first few weeks to avoid having to start over if you make fatal mistakes.

https://rewindio.grsm.io/quickbooks

Last resort, purchase a 3rd party service to assist your setup.