You can use the web interface to export a CSV file of all your data on the import export tab of your channel view. You can also use the REST API read data endpoint to export the data in a csv file. In the command, use the .csv ending. On the API keys tab or you channel or in the read data api documentation page, you can see the format.
https://api.thingspeak.com/channels/CHANNELID/feeds.csv?api_key=xxxxxxxxxxxxxxxx&results=2
