• Make sure all relevant file types are treated as PHP.
• Select Code > Run Inspection By Name, locate the inspection. Example: Old style constructor.
• In the next dialog, pick Custom scope, then Project, or click the ... button to create your own scope.
• Once the search is complete, select the warning group, then click on the button with the light bulb icon to automatically fix everything. Note that not all inspections can be auto-fixed.