VBA Command Button Macro

Ok, this is an interesting one I think.

I have a Worksheet, and a Macro which will load a User Form.

the User Form as 2 Combo Boxes, One lists peoples name (Found on WorkSheet 2) and another will list a type of Gear (Found on Worksheet 3)

I have a Button which needs to take the selected person from the first combo box, find there location on Worksheet 1 (Found somewhere in the A Column), and edit the corresponding cell in the D Column. I actually need it to take its current Value and Add a predetermines variable called TotCost

So what I need help with, is the code to do the Search for, and edit Corresponding Cell in D