Manually... you might want to open a ticket with Directadmin support for official instructions. Or search the forums for them. Some time ago (2-3 years in the past... or even more) I wrote a script exactly for these purposes, i.e. rebuild missing data.
Currently I don't have a link for the mentioned post from these forums, and don't have instructions which will work with updated awstats scheme.
Probably somedoby else from the forums have another tested solution.