I like the idea of telling Barry that Iris was going to Earth-X but then secretly taking her to a different Earth. By giving Barry false information that he does not know is false, it would use Savatar's knowledge of Barry's memories against him. Savatar would go to Earth-X and have to search the entire planet to find her when she is not there. He would waste a lot of time trying to find her and have no way of knowing which Earth she is on. Without any way to find Iris, Savatar would be unable to kill her, so it would save her life and it would buy Barry time to stop Savatar. Moreover, it if were impossible for Savatar to kill Iris, then Savatar would actually cease to exist since he needs her murder in order to be created.