Do you mean "change cell value" by "edit"? Editing is a process of changing a cell by the user, i.e. interactive action.
If you ask what is the fastest way to find the row with the required cell contents, then you can exploit row keys for that. Use the values you search by as row keys too, and then a call like iGrid.Rows["5098984"] will immediately return the required row object (iGRow). iGrid uses an optimized internal algorithm to search a row by its key (kinda binary search) - that's why this will work much faster than enumerating rows.