PC to arduino serial data sending

I am starter of the arduino and coding.
There are some problems that I cannot solve by myself, so I would like to get some advice from forum.
I am trying to control the LED by the heart rate.
If it is over 100, then it is ON, while not, then it is OFF.
The heart rate data is uploaded on the website dashboard, and i am success to get the data by OCR using c#.
The problem is the number is consistently change and I want to send the data serially to arduino, not writing data manually.
I am trying to do this using c#, however, i cannot find the method to send the data serially.
Now I wonder whether this is possible and if possible could you give me advice how to do?
Thank you.

You've had a look here ?

For receiving the data on the Arduino have a look at the examples in Serial Input Basics - simple reliable ways to receive data.