C# how to find word in textbox.text WPF

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C#

WPF

I need to find any word in textbox.Text.I have two textboxes,in first textbox i write any sentence, for example` Hi,how are you? and in second textbox i write any word, for example` "you",then when i click on button find, it must underline that word and say me that there is 1 word with Label.
Someone can help me how can i write this code with WPF.
Thank you.

What I have tried:

This is my code`

<Grid>
        <Button Click="button1_Click" x:Name="button1" Content="Find" Margin="185,180,146,140"/>
        <TextBox x:Name="textBox1" Margin="10,10,146,191"/>
        <TextBox x:Name="textBox2" Margin="10,180,296,140"/>
    </Grid>

private void button1_Click(object sender, RoutedEventArgs e)
       {
           int index = 0;
           string temp = textBox1.Text;
           textBox1.Text = "";
           textBox1.Text = temp;
           while(index < textBox1.Text.LastIndexOf(textBox2.Text))
           {
               textBox1.Select(index, textBox2.Text.Length);
               textBox1.SelectionBrush = Brushes.Red;
               index = textBox1.Text.IndexOf(textBox2.Text, index) + 1;
           }
       }

ScreenShot`
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