@Override is not allowed when implementing interface method
Solution 1:
If your project has multiple modules, also check that every module uses language level 6 or above, or use the project's language level (see Project Settings > Modules > xxx > Language level).
You may need to reload your project once it is modified.
Solution 2:
At your module/project, Right click to see context menu:
Choose Open Module Settings or press F4. In setting windows:
Set value for Choose Language level section.
You also should check Project language level by this way: press Ctrl+Alt+Shift+S