For the circuit, you need some software to hardware interface. The easiest to get started with that is to use the popular Arduino microcontroller board. There is an enormous number of tutorials online to to get the results you want.
Shows how to send commands to the board and receive a response:
https://www.arduino.cc/en/Tutorial/SerialCallResponseASCII
Shows how to blink an LED on/off, you can get the flicker frequency you want by adjusting delay times:
https://www.arduino.cc/en/tutorial/blink
The Arduino is programmed using a C-like language, however, lots of the functionality for serial communication is built into an easy to use library. There are alternative boards out there that can be programmed with Python that deliver similar results like CircuitPython (https://circuitpython.org/).
To communicate with the board via PscyhoPy, you can send command strings using the example Triggering from Serial port. From builder, you may need to use a “code component” to run the necessary commands (https://www.psychopy.org/builder/components/code.html).