let phs = ActivePresentation.Slides.Item(1).Shapes.Placeholders

if(phs.Count > 0){
    switch(phs.Item(1).PlaceholderFormat.Type){
        case ppPlaceholderTitle:
            phs.Item(1).TextFrame.TextRange.Text = "Title Text"
            break
        case ppPlaceholderCenterTitle:
            phs.Item(1).TextFrame.TextRange.Text = "Centered Title Text"
            break
        default:
            MsgBox("There's no horizontal title on this slide")
    }
}