zoho client script java script

I use Zoho crm, and I need someone who knows clients script (javascript). I just need some simple code written with client script which auto populates a field based on user selecting a field

I have a drop down field called "cruise types" if you select "9 day discovery" from the drop down, I want it to autopopulate another drop down which is the "cruise pick up time" to 4:00 pm,