If you have backed up before then you can restore as specified here..
To back up a site collection, run this command:
stsadm -o backup -url <url> -filename <filename>
where <url> is the url of your site collection and <filename> is the file you want to backup to.
To restore the site collection, run this command:
stsadm -o restore -url <url> -filename <filename> -overwrite
where <url> is the url you want to restore the backup into and <filename> is the backup file.
The -overwrite flag is used to overwrite the existing site if it already exists. However be careful that you don't overwrite an existing working site. You can always run the restore first without the -overwrite flag to determine if you need the overwrite flag. The command will let you know if an existing site is already located at the url you specified. During my testing, I restored a site in the wrong place with the overwrite flag completely killing the original site. Thankfully I backed up everything before I made any changes