i want to have a macro code change based on input from a textbox in a form

so I have this code and I want the "100" that's show in red to change based on input from a textbox in a form..

my form is called "qtyform" the textbox is "qtybox" and the form also has a "enter" button called "enterbutton"

thank you!!

Option Explicit

Sub MatchAcrossSixWorkbooks()
Dim MyWb As Variant, WasOpen As Boolean, wbOPEN As Workbook, MyNum As Double

MyNum = ThisWorkbook.Sheets("Numbers").Range("H13").Value + 100
[/COLOR]On Error Resume Next

For Each MyWb In Array("Group1.xlsm", "Group2.xlsm", "Group3.xlsm", "Group4.xlsm", "Group5.xlsm", "Group6.xlsm")
    
    Set wbOPEN = Workbooks(MyWb)
    
    If Not wbOPEN Is Nothing Then
        WasOpen = True
    Else
        Set wbOPEN = Workbooks.Open(ThisWorkbook.Path & Application.PathSeparator & MyWb)
    End If
    
    wbOPEN.Sheets("Numbers").Range("H13").Value = MyNum
    
    If WasOpen Then wbOPEN.Save Else wbOPEN.Close True
    Set wbOPEN = Nothing
    WasOpen = False

Next MyWb

End Sub