Need guidance in evaluating cells and process another XLs to fill drop box list

I am working on a project using 2 xls files,

xls 1 used by maintenance and contains macro, hidden worksheet (data for drop down list) and a form.
xls 2 hold list of all properties.

In xls 1, I have 2 drop box inspector and properties. The inspector drop box is populated from the hidden worksheet, i have 3 columns that holds 10 inspector names:-

C1 C2 C3
Name Job Title Area/region
Inspector 1 Position 1 NEYH
Inspector 2 Position 2 MEE

...etc

in xls 2, locked master property data, updated on a regular basis, containing 8 columns:

LL name, LL email, property code, address1, address2, post code, status, area/region

problem:

In xls 1, when the inspector selects his/her name from the drop down list (setup to show only C1 data), how do i identify value in C3 and then use it to examine xls 2 to populate the second (properties) drop down list in xls 1.

So that the second dropbox does not show all properties, only specific to his/her area/region.

Appreciate any pointer or guidance.