How it's done:
1. Ensure that the ECU (Select) and WARI (tuning software) are properly talking to each other. That is, the USB communication is working properly. WARI should show you which specific ECU is connected if the USB comms are fine.
2. Do a "File + Log" using the software menu or just hit the Ctrl key + L as a shortcut. It will then prompt you to save a *.csv file with a default file name of the current date and time. You can change the file name to your preference, but please do remember where the file will be saved. (Tip: It might be easier to remember if you save it somewhere obvious e.g. Desktop, Documents, etc.)
3. You will know the ECU's in logging mode when the ECU status in WARI says so. This is the time to reproduce what you want to be logged.
4. When you're done reproducing the issue that needs to be logged, just do a File + Stop Log in the menu of hit the Ctrl key + K to stop the logging mode.
We normally ask people to send the log file(s) together with a copy of the current ECU file, so we can look at them side by side. Grabbing a copy of the ECU file is as simple as doing a "File + Save as" in the menu.
That's it! Cheers.