Subtract a textbox value from a cell - excel

Question

I have an inventory sheet.
When a researcher takes a quantity in a specific lot, the quantity is removed first from the stock quantity, the specific row of ComboBox1 in the column #8. It's okay for that part.
When a second quantity is taken and the row of the lot is not empty, I put the data in a row under but I want the quantity (textBox2) to be substract to the column #8 of the row of ComboBox1.
Private Sub CommandButton1_Enter()
Dim emptyRow As Long
Dim ws As Worksheet
Set ws = ActiveSheet
ActiveSheet.Name = "Micrux"
Dim iLastRow As Long, iFound As Long
Dim rng, bEmpty As Boolean, c As Integer
Dim Test As Boolean
bEmpty = True
With ws
iLastRow = .Range("A" & .Rows.Count).End(xlUp).Row
Set rng = .Range("A1:A" & iLastRow + 1).Find(ComboBox1.Value, _
After:=.Range("A" & iLastRow + 1), _
LookIn:=xlValues, _
lookat:=xlWhole, _
searchorder:=xlByRows, _
SearchDirection:=xlPrevious)
Test = (TextBox2.Text) > ws.Cells(iLastRow, 8)
If Test = True Then
MsgBox "Not enough quantity in stock!"
Else
If rng Is Nothing Then
iFound = iLastRow + 1
Else
iFound = rng.Row
For c = 4 To 7
If Len(.Cells(iFound, c)) > 0 Then bEmpty = False
Next
If bEmpty = False Then
iFound = iFound + 1
.Cells(iFound, 1).EntireRow.Insert xlShiftDown
.Cells(iFound, 7).Value = TextBox2.Text
.Cells(iFound, 6).Value = TextBox3.Text
.Cells(iFound, 5).Value = ComboBox2.Value
.Cells(iFound, 4).Value = TextBox1.Text
Else
.Cells(iFound, 7).Value = TextBox2.Text
.Cells(iFound, 6).Value = TextBox3.Text
.Cells(iFound, 5).Value = ComboBox2.Value
.Cells(iFound, 4).Value = TextBox1.Text
End If
End If
End If
End With
Unload Me
End Sub