[c#] Editing an item in a list<T>

How do I edit an item in the list in the code below:

List<Class1> list = new List<Class1>();

int count = 0 , index = -1;
foreach (Class1 s in list)
{
    if (s.Number == textBox6.Text)
        index = count; // I found a match and I want to edit the item at this index
    count++;
}

list.RemoveAt(index);
list.Insert(index, new Class1(...));

public changeAttr(int id)
{
    list.Find(p => p.IdItem == id).FieldToModify = newValueForTheFIeld;
}

With:

• IdItem is the id of the element you want to modify

• FieldToModify is the Field of the item that you want to update.

• NewValueForTheField is exactly that, the new value.

(It works perfect for me, tested and implemented)

You don't need to use linq since List<T> provides the methods to do this:

int index = lst.FindLastIndex(c => c.Number == textBox6.Text);
if(index != -1)
{
    lst[index] = new Class1() { ... };
}

After adding an item to a list, you can replace it by writing

list[someIndex] = new MyClass();

You can modify an existing item in the list by writing

list[someIndex].SomeProperty = someValue;

EDIT: You can write

var index = list.FindIndex(c => c.Number == someTextBox.Text);
list[index] = new SomeClass(...);

class1 item = lst[index];
item.foo = bar;

1. You can use the FindIndex() method to find the index of item.
2. Create a new list item.
3. Override indexed item with the new item.

List<Class1> list = new List<Class1>();

int index = list.FindIndex(item => item.Number == textBox6.Text);

Class1 newItem = new Class1();
newItem.Prob1 = "SomeValue";

list[index] = newItem;