Excel ActiveX checkbox linked to cell on separate sheet

I have a very large matrix with employees in rows and training objectives in columns. I have managed to pull each objective and employees name in rows and columns. I am trying to create a form where checkboxes will populate the matrix. I cannot seem to link the checkbox with the matrix cells.

My variables give the correct information when sent to a MsgBox, I just can't figure out the checkboxes.

Private Sub CheckBox1_Click()
Dim r As String
Dim c As String
    r = Range("MatrixUpdate!H2").Value
    c = Range("MatrixUpdate!Q7").Value
    
Worksheets("Matrix").Cells(r, c).Value = CheckBox1.Value

End Sub

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