Recover missing log of AWstat

First you need to find the AWStats config file. It is called awstats.your_domain.conf where your_domain is usually your domain name.
C:\AWStats\wwwroot\cgi-bin

In the config file, you will find the DirData directive:
DirData="D:/Inetpub/wwwroot/cgi-bin/stat/awstats.domain.com"
it defines the directory where AWStats stores its database files.
To rename the database files, replace their .txt extension by .test (for example).
D:\Inetpub\wwwroot\cgi-bin\stat\

There is no magic solution to your problem. You need to have access to all the IIS log files of the month and to re-run the update for each day. Before you do that, rename the existing AWStats database file for the month (or delete it or move it to another directory). If the month you are updating is not the present month, you need to temporary rename all other months after the month of the update period as well.

Note that you can specify the path and name of the log file in the command line like in this example :

awstats.pl -config=servername -update -LogFile=C:/IISLogs/www/W3abc/ex080510.log

C:\AWStats\wwwroot\cgi-bin>awstats.pl -config=aoce2010.com -update -LogFile=D:\D
omains\LocalUser\aoce2010.com\logs\W3SVC70004\ex090806.log
Update for config "C:\AWStats\wwwroot\cgi-bin\awstats.aoce2010.com.conf"
With data in log file "D:\Domains\LocalUser\aoce2010.com\logs\W3SVC70004\ex09080
6.log"...
Phase 1 : First bypass old records, searching new record...
Direct access to last remembered record is out of file.
So searching if from beginning of log file...
Phase 2 : Now process new records (Flush history on disk after 20000 hosts)...
Jumped lines in file: 0
Parsed lines in file: 279
Found 4 dropped records,
Found 44 corrupted records,
Found 0 old records,
Found 231 new qualifed records.