I have just the steps you'll need to download and match bank transactions from 2018, see below:
Uploading Transactions with Bank Files
Begin by navigating to your bank's website and signing in. Locate your account's transaction list and look for a Download ⇩ button. Be sure to select one of the supported formats from the picture below.
In QuickBooks Online, click the Gear icon (⚙) and select Import Data. Choose Bank Data.
Click Browse and navigate to where you saved the bank file. Follow the on-screen instructions from there to map and import your data.