So it sounds to me, but correct me if I’m wrong, that you don’t know how to create the virtual device. 
You’ll need to do that with an edge Driver since the old method is being discontinued by smartthings in the next few months.
It would probably be a good idea for you to read about what edge is, as well as the steps for adding an edge driver to your hub
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
once you understand how to add an edge driver to your hub, you just need to find the right edge Driver to add so you can create the right kind of virtual device
The wiki article included the following section
Code for a Virtual Device which will Show Up as Both a Contact Sensor and a Switch
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The following post includes the code for a virtual contact sensor which is also a switch, so you can use that one. forum post including the code for a virtual sensor/switch
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If you have never used custom groovy code before, see the article on how to install custom groovy code to your account.
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‘’2022 Update’’
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Since SmartThings’ support of Groovy code will be going away soon, if you are interested in trying the Beta Edge Driver as your virtual device (Edge Drivers replace groovy DTHs in the new architecture), see the following thread:
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VEdge Creator
Just ignore all the stuff before the “2022 update“ header. That’s going to be out of date within a few weeks.
When you are ready to create the virtual device, you should follow the link to the Vedge creator.
You will then use that to create the virtual device. If you have read the edge FAQ I just gave you the link to and you still have questions about how to create the virtual device, ask in the Vedge Creator thread and someone there will help you.
Once you have created the virtual device which is both a switch and a sensor, you will be able to use the process I gave you in my first post.
Hopefully that helps. 
If I’m wrong, and you already created your virtual device, but you still don’t know how to use it, please specify which of the four steps in my original post you were confused about.