Place a command button in a cell MS Excel vba

You can't place any object "in" a cell, only over it. You can set the button's Left and Top properties to the Cell's Left/Top.

Sub Tester()
    Dim rng As Range
    Set rng = ActiveSheet.Range("B3")
    With ActiveSheet.OLEObjects("CommandButton1")
        .Top = rng.Top
        .Left = rng.Left
        .Width = rng.Width
        .Height = rng.RowHeight
    End With
End Sub