It sounds like you have combined two different Questions into one.
Under the old architecture, the one that is scheduled to be discontinued beginning September 30, you could use the IDE to add a “custom device type handler“ or “DTH.”
The IDE itself is being discontinued But you should still be able to access it until October 15.
So the answer to the question “How do I get to the IDE now?,“ is in the following thread. But remember that anything you add that way is going to stop working very soon now.
FAQ: How do I access Smartapps, Devices, etc. from web (the old IDE information)
Groovy DTHs are going to be replaced by “Edge Drivers” written in Lua which run locally on your own hub. Installation of custom Edge Drivers is easy. You will just follow a link that the author gives you and select the driver and it will be download it to your hub.
For more information about that:
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)
But you Don’t install a “driver“ (new architecture) from the IDE (old architecture), so I’m not quite sure what you’re asking.
What’s the brand and model of the device and where did you get the information about the code that you would need for it? 