If they directly stole copyrighted assets you could just send a DMCA request to have it taken down. They didn't do that so this is all probably frivolous.
But what about the profit that has already been made? Apple is taking 30% after all.
If they aren't copyright infringing, then the profit is theirs. I don't think that any assets were directly stolen, and these games just look and play like PUBG.
That's only one remedy available, this is another one.