I just downloaded xcode 9 beta, but there is no simulator within it. Try to add new simulator but the create button doesn't work. Please help
By "no simulator within it" I mean there is option to build with simulator.
Go to Xcode Preferences -> Locations and go to the Derived Data location in Finder:
Just remove all contents from it, then right click on Xcode icon and quit it, and reopen it: