GCODE used to help with manual leveling of the ender 3 print bed.

E3_Bed_Level.gcode

; THIS ASSUMES YOUR PRINT BED IS THE SAME SIZE AS STOCK THE ENDER 3
; Author: Colin Andress
; Last modified date: November 2nd 2020

G28 ; Home axes
G21 ; Set units to MM just in case
G90 ; Set positioning to absolute mode

; Y:15, X:15
G0 Z10.0 F3000 ; Move Z to 10mm
G0 X15.0 Y15.0; Move X and Y to 15mm
M0 Place paper below nozzle ; Wait for the user to press the LCD knob to continue
G0 Z0.0 ; Move Nozzle down to the bed
M0 Adjust level ; Wait for the user to adjust the axis level

; Y:215, X:15
G0 Z10.0 ; Move Z to 10mm
G0 Y215 ; Move Y to 215mm and Z to 10mm
M0 Place paper below nozzle ; Wait for the user to press the LCD knob to continue
G0 Z0.0 ; Move nozzle down to the bed
M0 Adjust level ; Wait for the user to adjust the axis level

; Y: 215, X:215
G0 Z10.0 ; Move Z to 10mm
G0 X215 ; Move X to 215mm
M0 Place paper below nozzle ; Wait for the user to press the LCD knob to continue
G0 Z0.0 ; Move nozzle down to the bed
M0 Adjust level ; Wait for the user to adjust the axis level

; Y:15, X;215
G0 Z10.0 ; Move Z to 10mm
G0 Y15.0 ; Move Y to 15mm
M0 Place paper below nozzle ; Wait for the user to press the LCD knob to continue
G0 Z0.0 ; Move nozzle down to the bed
M0 Adjust level ; Wait for the user to adjust the axis level

G0 Z10.0 ; Move Z to 10mm
G0 X25.0 Y25.0 ; Move X and Y to 25mm
M0 Leveling complete. Press to continue ; Wait again for the user to press the LCD knob

Revision 1: Added a feedrate tweak to hopefully make moves faster. Can probably even be faster, but this is a good middle-ground for most people's setups.

Depreciated Please generate your own GCODE using this tool I made: https://github.com/Column01/Bed-Level-Generator