In \garmin\apps\logs create a file called <your app prg name>.txt, then in your app just use Sys.println(), etc. You'll get what you see in the console with the sim.
There are limits to the file size, and writing to a log file is expensive. This is really a debug function and not a production thing.
Also, when something is installed from the store, <your app prg name> is generated by the store (an 8 char string), so it's hard to tell a user what the name should be so they can create the .txt.
What do you want to do with the extra data? Maybe for your use case you just need to know the steps made during your activity and writing it as part of your fit file with the FitContributor would be a better option?
I have more other data to record. It's for an experimentation, for example when a message display on watch, I save the time as the participant make to push the button "key-esc" and I would save more other data like this in a text file (csv format) to compare data on excel.
