Hello there, treasurer,
Let's make sure your previous downloaded transactions are still there in your QuickBooks account.
The bank transactions in QuickBooks Online (QBO) will remain in the system regardless if you've disconnected the bank, and/or re-connected it with a new login.
To check, here's how:
After performing the steps above, you'll be able to view all your historical data in QuickBooks.
In the future, if you want to download transactions from your financial institution, you can go through these articles:
Please don't hesitate to leave a comment if you have further concerns about viewing historical transactions in QuickBooks. I'm just around if you need help.