Create a function to clear UserForms VBA

I am creating a program which has several UserForms. At the end of the program I need to clear every Checkbox inside some UserForm. I have created a Function, but it cannot recognise which UserForm it should clear, can you help me there? Here is the code:

Function ClearUserForm(ByVal userf As String)

Dim contr As Control

For Each contr In userf.Controls

If TypeName(contr) = "CheckBox" Then
    contr.Value = False
End If

Next

End Function

And I am calling the function like this, for example:

ClearUserForm ("UserForm2")

It seems not to recognise in which UserForm it should work.