since the date you are receiving is a number not a date so you can't apply date functions directly, you have to trim the number as:
mid(CYYMMDD,2,2) as year;
mid(CYYMMDD,4,2) as month;
mid(CYYMMDD,6,2) as day;
Date(MakeDate('20' & $(year),$(month),$(day)),'DD/MM/YYYY') as date;
you get the required date.