Godot is the open source game engine that Thrive is built with. Godot resources, such as .tscn files, need to be modified in its editor.
If you have never worked with Godot before it is recommended you start with the official documentation, specifically the step by step section which goes over the basics of how the engine works. Additionally you should look at the C# scripting section since that is the language used by Thrive.
The Class Reference is a resource that should be used often by programmers, it contains information on all of the properties, methods and signals of each of Godot's nodes. By using an IDE that works well with Godot you can see the class reference directly in the IDE while coding.
If you learn better with videos GDQuest is a well known and high quality Godot tutorial channel. In addition there are many other channels on youtube, just search for the feature you want to know more about.