How to fill second dropdown on the base of first dropdown va

I have tow following dropdowns and I want to fill second dropdown on the base of first dropdown value.

 

Select… Drilling Gas Select… Drill1 Drill2 Compression Dehydration

 

When I click Drilling option in iFunction dropdown then I want to fill Drill1 and Drill2 in another dropdown on the base of 1 common in both the dropdown list.

 

i have tried many approaches provided by Google

Can someone suggest me approach?

Thanks.