Changing label text from another form

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form

My code below:

private frmintro intro;

Main Form1:

private void pictureBox3_Click(object sender, EventArgs e)
        {           
            intro = new frmintro();
            intro.LabelText = "LabelChanged!";
            intro.Show();
            
        }

another form:

public string LabelText
        {
            get
            {
                return label1.Text;
            }
            set
            {
                label1.Text = value;
            }
        }

My code works, it changes the label text, but it creates another form and its floating out of panel.

What I have tried:

So i docked the panel using:

private void pictureBox3_Click(object sender, EventArgs e)
        {           
            intro = new frmintro() { Dock = DockStyle.Fill, TopLevel = false, TopMost = true };
            intro.LabelText = "LabelChanged!";
            intro.Show();
            
        }