I have a theme that needs some customization

I have a theme with a search function that needs a little tweak.
Current search function:

Category and subcategory in same field (subcategories are arranged in hierarchical or ID)
Location and sublocation in same field (sublocations are arranged in hierarchical or ID)
(See attachment for current search function)
I would like subcategories and sublocations to be shown in separate fields respectively upon selecting parent.

For example:
Select Category: Smart Phones
Select Sub Category: iPhone
Select model: iPhoneX

Select Country:
Select State:
Select city:

See Attachment 22