Your control exposes a method, probably named Plot. You can easily see what
Methods and Properties the control exposes.
Open any code module.
Right click anywhere in the code window and select Object Browser.
In the Topmost left Combo control which currently shows <All Libraries>
select your ActiveX control's library.

Now you can see all of the components of the library and how to read/write
the Properties and call the Methods of the specific class.

Place code behind your CommandButton like:

Me.NameOfYourActiveXControl.Plot ProbablyAParameterForTheMethodHere

If you are still having trouble, from the Object Browser window copy and
paste the Plot method declaration.
For example, here is the VBA lib MsgBox function.

Function MsgBox(Prompt, [Buttons As VbMsgBoxStyle = vbOKOnly], [Title],
[HelpFile], [Context]) As VbMsgBoxResult
   Member of VBA.Interaction