You can manually create your transactions with the dates before you started your QuickBooks account. This way, they'll be reported as your historical transactions into your books.
To start with, you can create a sales receipt or invoice as the transaction for your historical income. You can do so by clicking the Plus icon and selecting Sales Receipt or Invoice under Customers. Simply make sure to manually enter the date of your transaction before you started creating your account.
Meanwhile, here's how you can manually enter your historical mileage:
Go to Mileage.
Tap Add trip.
Under Trip date and time, manually enter the date of your mileage.