change the tab event to enter event

If I understand you correctly, You want to change the input that some Control receives.

I would try that by subclassing the target Control and override its OnKeyDown event:

protected override void OnKeyDown(KeyEventArgs e)
{
    if ((e.KeyCode & Keys.Tab) != Keys.None)
    // "Tab" was pressed
    {
        e.KeyCode &= ~Keys.Tab;     // Forget "Tab"
        e.KeyCode |= Keys.Enter;    // Use "Enter" instead
    }

    base.OnKeyDown(e);
}

That should make the derived class act as if "Tab" was an "Enter" as well.