How to I download all 12months of transactions not just last three months?

Welcome to the Community, familylife.  I'm here to help you download the transactions in QuickBooks Online (QBO). 

When you connect your bank to QuickBooks, the system downloads up to the last 90 days of transactions. To download older transactions, you'll have to upload them manually into your account. With just a few clicks then you're all set.

Before doing so, let's download the old transactions from your bank's website. Then, map the transactions in the following supported formats or file types. Once done, start importing the transactions so they become available in your Bank Feeds. Please follow these steps:

1. Go to Transactions or Banking on the left panel.
2. Within the Banking page, click the Link account drop-down arrow.
3. Select Upload from files. Another window will appear.
4. Click the Browser button. Then, select the file saved from your bank.
5. Hit the Next button.

I've added screenshots for your reference. 

I've attached here an article to guide you with the process: How to upload more than 90 days of bank transactions?

Once the transactions are in, I recommend categorizing and matching the transactions to the existing entries in QBO. Doing so will help ensure your financial records are accurate. Just go to the For Review tab to complete this task. 

Please keep us posted if you need additional assistance in managing your transactions in QuickBooks. We want to make sure your books are accurate.

@familylifeteambu 

Another option, use MT Online or one of the converter tools (e.g csv2qbo @ $60 one time license) as a workaround.

https://www.moneythumb.com/?ref=110