Hi Apostolis,
Thank you for your interest in Syncfusion products.
You can select the Tab in TabbedMDIManager programmatically by using SelectedTab property. Please refer to code snippet given below which demonstrates how to select the Tab programmatically.
tabCtrl.SelectedTab = this.tabbedMDIManager1.GetTabPageAdvFromForm(frm2);
Please refer to the attached sample given below:
http://websamples.syncfusion.com/samples/Tools.Windows/F73077/main.htmPlease let me know if you have any questions.
Regards,
Vinoth