Basically if you make the cells the checkboxes are linked too 'TRUE' all checkboxes will be checked
So... the following code should work.
Just assign it to a button:
Change the range to fit the range where your cell links are....
Sub CheckAll()
Dim MyRange As Range
Set MyRange = Range("H12:H16")
For Each c In MyRange
c.Value = True
Next c
End Sub