Hi Lisa CONYERS,
Welcome to Quickbooks Community.
To download bank transactions from the previous year, you have to go directly to your bank's website to check if the data is available for download. If not, you will have to contact your bank and request a copy of the transactions from previous year. Once you have the copy of the bank transactions, we will manually import them. Please refer on this article link on how to format csv file and upload bank transactions to Quickbooks Online.
Feel free to reach out to us if you have questions.