I was in the same boat as a lot of you asking for this solution. I figured out a way that helped me, so maybe it can help you.
First off, I used Coinbase for my cryptocurrency. In order to upload a CSV file to Turbotax, you have to login, then click on your profile "logo".
Click on "Taxes and Reports".
Scroll down to "Other Reports"
Find the link correlating with your "Gain/Loss" report for the current year.
Click "Download"
A long list of all the wallets from Coinbase (whether I traded that currency or not) appear.
Right Click "Download" under the currency you want.
Choose "Download Linked File"
You will find the file under downloads on your computer.
When asked by Turbotax to attach a CSV file I chose the file I just downloaded. (I only uploaded my BTC wallet because although I also traded with LTC and ETH, their wallets didn't show any transaction history on their respective CSV files).
Pro Tip: Download the currency wallet CSV files for the currencies you traded with. Then go to your file explorer on your computer and open each one. Check to see if there's any transactions on it. If there aren't any transactions listed, (i.e. date, amount, type, sold, etc.) then don't upload it to Turbotax.
Hope this helps some of you
