Using Instr in find and replace

I am currently using the following code

Dim x As Integer
Dim FindString As String
Dim ReplaceString As String
Dim NumRows As Integer
With Sheets("FindReplace")
    .Activate
 NumRows = Range("A2", Range("A2").End(xlDown)).Rows.Count
  Range("A:A").Select
  For x = 1 To NumRows
     FindString = ActiveCell.value
     ActiveCell.Offset(0, 1).Select
     ReplaceString = ActiveCell.value
     ActiveCell.Offset(1, -1).Select

     With Sheets("Sheet 1")
        .Activate
        Cells.Replace What:=FindString, replacement:=ReplaceString, LookAt:=xlWhole, SearchOrder:=xlByRows, MatchCase:=False
        End With
     Sheets("FindReplace").Activate
  Next
End With

I have set up a separate sheet with all of the find and replace values.
However what I really need is for the macro to find the values anywhere in the cell and replace it eg.
Right now
France - FR and France/USA stays the same
Would like
France/USA - FR/USA
Ideas?
Thanks