how to set PYTHONPATH to default value in ubuntu 20.04

I want to reset my python path. When i try echo $PYTHONPATH, I am getting /home/guru/noetic_robots/turtlebot3_ws/devel/lib/python3/dist-packages. I don't know how this happened

I have python 3.8 and 2.7 installed on my PC with Ubuntu 20.04

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