How can we Dynamically update the pixel into occupancy map?

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When running the Navigation Node, the lidar is at the top of the robot(Turtlebot3), I added a sonar sensor at the bottom of the robot in order to detect the small objects in front of the robot(lidar at the top can't see that). Now I wanted to dynamically update the pixel into occupancy map while running Navigation node when sonar detects small objects at the bottom?

I attached the Image in order to describe this better.