Thank you for your post.
If you downloaded FileMaker Go 12 to iTunes, then you can connect your iPad to iTunes and copy FileMaker Go 12 from iTunes back onto the iPad. If you only downloaded FileMaker Go 12 through the App Store, then you won't be able to download FileMaker Go 12.
Also, check GoZync to see if there are any updates for FileMaker Go 13.
Please let me know what steps you took to corrupt the file in FileMaker Go 13 so I can test it out and get it reported.
I still have clients using iPad first generation and are just now using my database service, now they will not be able to use my database unless they spend 500 to buy a new iPad as FMGo 13 is not compatible with iPad 1. Please bring FMGO 12 back.