Let me share some information about how your bank transactions are downloaded into QuickBooks.
May I ask for the name of the bank you're working on? Just a heads-up, when connecting your bank with QuickBooks, the system depends on the data your bank shares with us. However, it automatically downloads 90-days worth of your transactions during the first time you connect it. However, some financial institutions shares a year worth of transactions.
Also, you need not to worry, you can download and import the rest of your transactions using a CSV file. Here's a screenshot of sample file format that you can use:
4 Columns
3 Columns
Once completed, you can start the importing process. Here's how:
Go to the Gear icon.
Choose Imports.
From the Import transactions page, select the account where you want to record the transaction.
Click the Import older transactions link.
Browse to the CSV file on your computer and click Open.