How to keep the value of the text box in the combo box

Let say i have a field called Status
when you create a  record, the status is "Intern"
so txtStatus.text="Intern"
I have Update button, it will open combo box Status with prefileed statutes :
Intern
Part Time
Full Time

so you have the ability to select something from the combo box and update the status, from Intern to Part Time or what ever...
But the original status should be preselected in combobox