We can do this by using childitem.
The syntax is Obj.childitem(rowno,colno,ClassOfTheObject,index)
Ex: Here is the example to check a checkbox in 4th row, 2nd col.
set cbObj=browser(browserObj).page(pageObj).webtable
(webtableObj).childitem(4,2,"WebCheckbox",0)
cbObj.set "ON"
