Try cleaning your build folder. The keyboard shortcut is Shift + Command + K
The other thing you could try is to close your project and in Finder navigate to your Xcode DerivedData folder and remove the project entry from there. This is where Xcode builds (complies) your project and is where it creates the executable version to load into your simulator.
Deleting it is no problem as it will be re-created the next time you open the project in Xcode but the contents will be fresh and unaffected by any previous code.
The simplest way to navigate to that folder is to go to your Finder menu and tap on the menu option Go > Go to Folder.
Copy and paste the following into that field:
~/Library/Developer/Xcode/DerivedData/
and tap on Go
Scroll through contents of that folder until you find your project. Move it to the bin.
This action may not solve the issue but it’s good house keeping nevertheless.