There are two files. First run the CHEP_Ender_3_bed_level.gcode file on your Ender 3 or any similar size printer. Adjust each corner by running a piece of paper or Filament Friday sticker under the nozzle until you can barely move it.
Then run the Sq_bed_level_test.gcode file and live adjust or "adjust on the fly" the bed level knobs to get as close to a level bed as possible.
Then stop the print and you are ready to 3D print without worry about bed level.
All this is explained in my YouTube Video: