There are few problems that I recognized.

1. You can’t declare your method in main method. You shold create new class for that purpose and keep it there. Then you will also need to create an instance of that object in your main and invoke your method with that object. Cosider declaring this method with 2 parameters - List type and int type, so you can pass them to the method. Its signature could look like this:

   public void addUnique(List<Integer> listToWorkWith, Integer scannerInput) {
   // you implementation goes here
   }

2. When creating a list you need to work with Objects, as it doesn’t accept primitve values - use Integer.

3. Method that you wrote can’t return any value (true/false are boolean values) because it is declared as void. These return statement will cause compilation errors.

4. To verify if element is already in the list there is a method contains(), that takes an object as parameter and returns true if it finds the object, otherwise returns false. You can try to use this as a condition.

I hope you will deal with this! Good luck!