These instructions are for Turbotax Online.
If you are using the CD/DVD version of Turbotax then you should download the Turbotax CD/DVD report from Koinly which will give you a .txf file that can be easily imported into it.
1. Download the Turbotax Online report from Koinly
2. Login to Turbotax and go to the Wages section
3. Scroll down to the Investment Income section and click on it, this will drop down more options. Click on Start or Revisit next to the Cryptocurrency line.
4. Click on Add More and then select Coinbase (any of the other options will work too) and click on Continue at the bottom.
5. Upload the Turbotax Online report you downloaded from Koinly here and click on the Continue button at the bottom.
6. On the following page click on Select All and then on Continue at the bottom.
That's it, now all your transactions have been imported to Turbotax!
If you have more than 2250 transactions:
Note that Turbotax has a limit of 2250 transactions so if you have more than this, Koinly will aggregate your transactions keeping the long-term and short-term gains the same. You might want to attach the Capital Gains Report with your tax-return in such cases.