Problems connecting Arduino MKR Zero to External Modbus Master application

I'm struggling to get a modbus master application to communicate with the arduino mkr zero through an RS485 adapter via serial. I have all the code for the master application but I'm not sure if I need to incorporate any of that into the arduino IDE in order for everything to communicate?

I found an arduino slave library online and it compiles properly.

I was able to set up serial to serial communication, so I know everything is working and ready to communicate, it's just knowing where to begin with the programming.

I know everything I'm describing is very general but I just need a bit of guidance.

you begin with an example of the modbus library

Try the basic example from from your RS485 Arduino Library and then understand the code line by line. Try using Arduino debugging tool i.e. Serial Monitor. Print your values on serial terminal, it helps in understanding the flow of code.

Share your code here and ask questions from it and members will help you as well in understanding the code.