I once extracted single apps and apps data using a normal archiver explorer in my Arch Linux system. In Windows, 7-Zip FM or Winrar should do the trick.
Obviously it is quicker done if you restore the full backup all at once with a custom recovery (but I believe you already merged the archive parts the backup is done in), but I once made a backup after the system launcher went to a systematic crash, so I couldn't do anything, and doing a full restore would led to the very same problematic, so I had to get back the data of the apps I wanted to restore that way.
Just open the
.tar files, they are compressed archives.
data.tar contains what the
data folder contains in your Internal Storage: upon all the folders,
data/app contains the apk of the applications you have installed, and
data/data their saved data, which is you may want to restore. Inside that folder, every app has its dedicated folder (e.g.,
Google Maps). Copying it in your
data/data folder in your phone with a root file manager will restore the data for that app.
Again, for a complete restore, just copy the whole packages (supposing you left them untouched) in the directory they were (to find out which it is, do another backup and you will see where it is created), boot into a custom recovery like CWM Recovery and do a full system restore, pointing to where the backup is located in your phone.