Login To Your Gemini Account
Navigate to the History Page
Click the "Download History" Link
DO NOT open the file in Excel and "save as" a new file.
It's important to upload the raw file that Coinbase Pro exports straight from your "Downloads" folder. This avoids rounding errors and corrupting the file.
Upload your trade history file into the Gemini tab on Step 2 (Import Trades) and click the Import Trades button.