myFile = Application.GetOpenFilename(, , "Browse for Workbook")
    Set tws = Workbooks.Open(myFile)

Public tws      As Workbook

myFile = Application.GetOpenFilename(, , "Browse for Workbook")
Set tws = Workbooks.Open(myFile)

LastrowTar = tws.Worksheets(2).Cells(Rows.count, 2).End(xlUp).Row
Set tarRng = tws.Worksheets(2).Range("B3:B" & LastrowTar)

Sub getFile()
myFile = Application.GetOpenFilename(, , "Browse for Workbook")
    Set tws = Workbooks.Open(myFile)
End Sub