Use picocom - sending request

With picocom you can communicate to a serial device. Once you open it, you have something similar to the arduino serial monitor but every character you type is directly sent to the arduino.
You can use putty if you don't like picocom commands.

The escape commands C-a means: CRTL+A

To quit picocom, first press CRTL+A followed by a regular x.

Press ctrl button and then without releasing it press a and then q. It will exit the picocom application.