How and what libraries need to be connected to unity in order to debug a third-party dll library?

Question

C++ / C#

I've been studying Unity for less than a week, and there was such a problem:
There is a dll library for the rules of chess games. I connected it to the unity script, and in this dll an error occurred in one of the methods. And I thought that you can connect the unity library to use the Debug class. Or what would be the best way to do it?