How to create a tabitem in another window's mainwindow

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C#

WPF

I'm new to wpf C# and I wanted to create a new TabItem in my MainWindow when I select the data in a separate window, is there a way to do that?

What I have tried:

Usercontrol TDados = new Usercontrol();
ClosableTab theTabItem = new ClosableTab();
theTabItem.Title = Dados._NomeCliente;
theTabItem.Content = TDados;
TabControl.Items.Add(theTabItem);
theTabItem.Focus();