Instance member ‘initSharedPreferences’ can’t be accessed using static access.dartstatic_access_to_instance_member

class SharedPrefHelper {
  SharedPreferences? sharedPref;

  Future<void> initSharedPreferences() async {
    print("Running get instance");
    sharedPref = await SharedPreferences.getInstance();
  }
}

when I tried to access this methos got an above error,
How to fix it?