Without knowing where all the save games are, the easiest way (although cumbersome) I can think of is to just enter a battle and then immediately delete your commander xD.
https://forums.uberent.com/threads/how-to-delete-broken-galactic-war-games.64020/ Try this if you have a bunch to clear. It still worked a couple builds back. I tend to let my no longer in us GWs build up then clear them all out at once. I hope the delete war button comes back soon though!
What happened to searching for threads before posting new ones? https://forums.uberent.com/threads/cannot-delete-a-galactic-war.67106/ https://forums.uberent.com/threads/how-to-delete-broken-galactic-war-games.64020/ https://forums.uberent.com/threads/how-to-delete-archived-galactic-wars-mac.61614/