i have a form with edit function. 1 combo box and 2 text box (txtbox1 and txtbox2)

txtbox1 show attribute from combo box value.
txtbox2, is for edit the combo box attribute in excel database.
i connect combo box with txtbox1 using vlookup function.

example :
combo box list :
1. A
2. B
3. C
4. D

if i fill txtbox2, and press the edit button, i want the value of txtbox2, will be replace value in txtbox1.
txtbox1 value it's get from database in another sheet.

please help, i've looking for 1 days long but still didn't know how to do it.
how to do it?