Creating a new SAS variable is basic DATA step programming with SAS. What code, if any, have you tried? Can you share that code for feedback? If you need to assign a new variable, you can do so in a SAS DATA step and since the variable is a DATE, you will want to assign a FORMAT statement to the variable (or use a singe ATTRIB statement).
I have provided a SAS-hosted documentation link below -- also, the SAS support http://support.sas.com/ website has very useful information as technical and conference topic-related references, which you can find using the SEARCH facility.