There is an option that allows you to correct the log files and on that is the daily rain totals, if you know the daily amounts then you can correct them in here.
Sadly I’m at work at the moment and not near my WD PC so I can’t give exact instructions but I’ll have a search around the forum and see if I can come up with something. 
Edit: See is this FAQ helps - http://discourse.weather-watch.com/t/27619