This is similar to the old Ender 2 bed leveling gcode, which I adapted to the Ender 3. Save the gcode to your SD card, and run it whenever you need to level. (Benchy STL is attached because of thingiverse requirements)

Be sure that your nozzle is clean or you wont be able to level correctly. No filament is extruded. Its not needed, and is rather wasteful imo.

The bed is first heated to 45 degrees. This is to prevent the deviation that comes from the metal expanding/contracting with the temperature change.

Then the gcode homes all axis, and moves to the first leveling point. Use the paper leveling method to adjust the bed to the correct height.

Once done, press the knob to continue to the next point. Paper level again. This cycles through the 4 corner points, 4 times.

Obviously there are other versions floating around on thingiverse. I needed one that cycled through each point more times, and heated the bed.