VBA To Choose The Source Cells For A List With Data Validation

when you choose Data Validation for a specific cell, you can choose list. Once you have chosen list for "Allow", you can select the source cells for what will be in the drop-down menu. I want to be able to use VBA (or just use Excel) to modify those source cells.

For example:

There will be 3 lists with drop-down menus using Data Validation.

List 1:
Choose first option in list -> List 2 uses source A
Choose second option in list -> List 2 uses Source B
etc...

List 2:
Choose first option in list -> List 3 uses source C
Choose second option in list -> List 3 uses source D