I am sure there is another simple way of doing this, but I usually convert the date to a string so I can extract what I want. So the syntax would be:
1. tostring var, replace
2. gen year=substr(var1, 1, 4)
3. gen month=substr(var1, 5, 2)
If you would like to put it together,
4. gen _newdate=year + month.