See if this works for you -
%// For demo couple of values are assumed, but these are the values
%// that you have got from excel file
numerical_vals = [35577 ; 35579]
date_array = datevec(numerical_vals);
date_array(:,1) = date_array(:,1)+1900;
out = datestr(date_array,'yyyy/mm/dd')
Output -
out =
1997/05/27
1997/05/29