Hi @Maria_pl , generally speaking the approach is as follows:
1. Generate a dummy flow file that will trigger (GenerateFlowFile processor)
2. Next step is UpdateAttribute processor that sets the start date and end date as attributes in the flow file
3. ExecuteScript is next. This can be a python script, or whichever language you prefer, that will use the start and end attributes to list out all the dates in between.
4. If your script produces single file output of dates, you can then use SplitText processor to cut each row into its own flow file and from there each file will have its own unique date in your range.
Hope that makes sense.