How to amend coding for Data Validation refer to a Named Range?

Dear Admin,

I am doing a combo box so that my data validation cell have so called Auto complete function. However, I don't not know how to amend a small part of coding to suit my needs. Please refer to below:

If Target.Validation.Type = 3 Then
    Application.EnableEvents = False
    'get the data validation formula
    str = Target.Validation.Formula1
    str = Right(str, Len(str) - 1) ' IF MY VALIDATION USING CELL REF, IT IS WORK, BUT_
    ALL MY VALIDATION USING NAMED RANGE, MAY I KNOW HOW TO AMEND IT TO    SUIT MY NEEDS?

Please advice me ! Thanks