There are different ways to use a Python library with Choregraphe boxes.
The best way: you can upload your library in the project content of your Choregraphe behavior. In Choregraphe, go to the Project Content widget, click +, import files, and select your library. You can also import a whole folder.
Then create a Python box, and inside you can write:
If your library is not to heavy, and you just need to use it once or twice, you can copy paste it in a Choregraphe box, then create a global or shared variable referencing the main object of your library, in order to use it in other boxes for instance.
This is, however, a very "sketchy" method that won't get you far, in my opinion