you set the needed correct rain total under control panel
offsets and initial rainfall setup
simple as that
you can also use the control panel, graph setup, graph correct, to remove the bad rain data from the graph (which then flows through to the data )
you can also reset the record rain rate
then if your logfiles are OK, get WD to re check for rain rate records, via action, convert logfiles to data files, tick, convert all
this question gets asked alot and there are lots of threads on the WD forum for how to do all this
and some FAQs too
I tell you what,
surprised at some of the comments here...some not very helpfull...