There are two options for importing your Coinbase trade history. You can upload your history via CSV files or import via read-only access API. The CSV process is laid out below.
Note - Coinbase and Coinbase Pro / GDAX are treated as two separate exchanges. If you used both, you need to import your history from each exchange. Here is the guide for importing Coinbase Pro.
*Very important to follow instructions exactly as seen to avoid errors*
Click on your profile icon and select Tools.
Select the Taxes & Reports tab from the tools menu bar.
Click on the Generate Report button next to Transaction History.
Click Generate Report with the following settings and then download the CSV Report.
Navigate to the Coinbase tab on CryptoTrader.Tax and drag the file you just downloaded into the blue box.