How to reset Data log to start, but keep setting?

2

AFAIK there are at least two possibilities:

  1. Delete the history and current data log via IoTaWatt-API: Graphs no longer working - #6 by overeasy
  2. Or download the config.txt file, insert the SD-card into your computer, remove all content and copy the SD files from the github site onto it and also your saved copy of the config file.