How to fire tab key event?

You can use Robot class for this

The following example shows how to simulate mouse and key presses in Java using java.awt.Robot class.

try {
    Robot robot = new Robot();
    
    // Simulate a mouse click
    robot.mousePress(InputEvent.BUTTON1_MASK);
    robot.mouseRelease(InputEvent.BUTTON1_MASK);
    
    // Simulate a key press
    robot.keyPress(KeyEvent.VK_SHIFT);
    robot.keyPress(KeyEvent.VK_TAB);
    robot.keyRelease(KeyEvent.VK_TAB);
    robot.keyRelease(KeyEvent.VK_SHIFT);
} catch (AWTException e) {
    e.printStackTrace();
}

Edited my post to do the SHIFT + TAB Key Press.

If what you really want is just to navigate to the next component, you can do:

KeyboardFocusManager.getCurrentKeyboardFocusManager().focusNextComponent();