Hey Bulut!
We don't have any apps that target tags specifically, but you can use our CSV export tool to get a spreadsheet of all of your products, including all of the tags associated with the products. You can simply edit them on the CSV, and then re-import them, overwriting your pre existing records of those products with a 'new' version that would include proper tagging.
Here are a couple docs to help you out with this:
http://docs.shopify.com/manual/your-store/6-products/5-export-products
http://docs.shopify.com/manual/your-store/6-products/6-import-products
Let me know what you think!
Matthew Buttler
Guru
Shopify Inc.