All actions performed in a timer are handled in the "Tick" event.
public partial class Form1 : Form
{
    Timer myTimer = new Timer();
    
    public Form1()
    {
        InitializeComponent();
        myTimer.Tick += myTimer_Tick; //assign the event handler named "myTimer_Tick"
    }
    private void myTimer_Tick(object sender, EventArgs e)
    {
        // Perform your actions here.
    }
}