Open file from location using VBA code - file name changes everytime.

Hi,
I need help to write a code to open a User name workbook from a location. This code should be in master file (Update_Report.xls) user will enter data in master file & press button to perform below actions.
Open perticular User name (Cell value B4 in Update_Report) excel workbook from location.
Copy data from master file.
Paste data in user file.
Save & close user file.

Code is as below. Code is not able to locate user file.

Sub Button8_Click()

  'Open user file & copy data

  FName = Range("B4")
  
  ChDir "C:\TEST\User Report"
    Workbooks.Open Filename:= _
        "C:\TEST\User Report\FName"
      Workbooks("Update_Report.xls").Activate
    Range("A1:B7").Copy
    Workbooks("FName").Activate
    Range("B5").Select
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Application.CutCopyMode = False

End Sub

I am not able to upload master file due to some error. After I press button "Manage Attachments" nothing happens.

Please help me with this.
Thanks in advance.

SWapnil