If you have a Windows computer, you can find it in the Pokemon Insurgence folder in your Saved Games folder. To get there, open up File Explorer and type “C:\Users” in the address bar at the top. Once you’re there, open up your user file (mine is just called “Owner”) and find the Saved Games folder. You can also search for Saved Games from your start menu. Once you get to the Pokemon Insurgence folder, you’ll see something like this:
If you’re running a Mac computer instead, check out this thread.
Game.rxdata is your current saved game. The other three are backups that the game makes every once in awhile. To switch your current game out for one of the backups, just rename Game.rxdata to something else (like GameOriginal.rxdata), then find the backup from a time before you sent your Blastoise to the GTS (probably the oldest backup) and rename it to Game.rxdata. Once you open the game again, that older save will be loaded.
I sure hope that you haven’t been playing too much after you sent TuffBoi to the GTS. The backups are often overwritten with new backups as you play, so hopefully one of them is far enough back. I hope this helps!
–Servant of the King