I don't think there is any way you can find this information yourself. You will have to contact the Machform development company which is Appnitro (although perhaps it has been renamed to Machform to match their primary product) and ask them to tell you which sites are using your license. As it says in the first message posted to this forum, "This forum is not an official MachForm support channel." so you cannot expect to get a reply from the developers here.
If you have an active support contract, log on to your billing account to ask for help. If your support has expired, you can try using this contact form. For the "How may we help you?" drop down, choose "Other". If you choose "I Need Machform Support", you will just be redirected to the Billing Area