Date format problem from an BI query

I have to different dates in 2 colums, this is a BI file and exported to excel, but now it seems that excel is not seeing this dates a valid date format? I uploaded the file can someone please assist. Cause if want to use formula to count the days in between and excel needs to see this a a proper date format. want to use formula =datedif(x1,y1,"D")
please help