Match one column data with data in the second column

I don't know if this can be done but I have a table with columns named Manager, Employee, EmpNum.

In a form created from the table, I have a 2 dropboxes, Manager and Employee.

How do I auto-populate a textbox with the EmpNum of the name chosen from the Employee dropbox?

It would be the same as a Vlookup in Excel.

If you are using a Form and that form is bound to your table then the relationship is already there and the text box on the form should automatically populate once you put in either the Manager or the Employee.