Flutter/Dart: update some variables but not others when using setState()

You can copy paste run full code below
You need to pass index not uid
You can adjust first and second number you want

code snippet

itemBuilder: (BuildContext context, int index) {
                  return roundCard(roundsList[index]);
                }),
...
onPressed: () {
                  uid++;
                  firstNumber++;
                  secondNumber++;
                  roundsList.add(
                      Round(roundNumber: uid, firstNumber: firstNumber, secondNumber: secondNumber));
                  setState(() {});
                }

working demo

full code

import 'package:flutter/material.dart';

class Round {
  int roundNumber;
  int firstNumber;
  int secondNumber;

  Round({
    this.roundNumber,
    this.firstNumber,
    this.secondNumber,
  });
}

int uid = 1;
int firstNumber = 2;
int secondNumber = 3;

List<Round> roundsList = [
  Round(roundNumber: uid, firstNumber: 1, secondNumber: 2),
];

class createLevels extends StatefulWidget {
  @override
  _createLevelsState createState() => _createLevelsState();
}

class _createLevelsState extends State<createLevels> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          centerTitle: true,
          title: Text(
            "Create Rounds",
          )),
      body: Padding(
        padding: const EdgeInsets.fromLTRB(20, 20, 20.0, 20),
        child: Container(
          child: Column(
            children: <Widget>[
              Expanded(
                child: ListView.builder(
                    itemCount: roundsList.length,
                    itemBuilder: (BuildContext context, int index) {
                      return roundCard(roundsList[index]);
                    }),
              ),
              Text("$roundsList"),
              RaisedButton(
                onPressed: () {
                  uid++;
                  firstNumber++;
                  secondNumber++;
                  roundsList.add(
                      Round(roundNumber: uid, firstNumber: firstNumber, secondNumber: secondNumber));
                  setState(() {});
                },
                child: Text("Add Round"),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class roundCard extends StatelessWidget {
  final Round round;

  roundCard(this.round);

  // roundsList.add(Round(roundNumber: 1));

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Card(
          child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            Spacer(
              flex: 1,
            ),
            Expanded(
              child: Text('Round ${round.roundNumber}:'),
              flex: 12,
            ),
            Expanded(
              child: TextFormField(
                textAlign: TextAlign.center,
                decoration: InputDecoration(
                  hintText: '${round.firstNumber}',
                ),
              ),
              flex: 3,
            ),
            Spacer(
              flex: 1,
            ),
            Expanded(
              child: TextFormField(
                textAlign: TextAlign.center,
                decoration: InputDecoration(
                  hintText: '${round.secondNumber}',
                ),
              ),
              flex: 3,
            ),
          ],
        ),
      )),
    );
  }
}

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: createLevels(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}