Assisted manual levelling with Marlin
Write a few pieces of gcode to do this. Place it on an SD-card (I assume you have a reader) and select the file you want to execute.

Home all:

G28
G1 Z0


Do you really want to home it directly? I would say you want to take it down slowly and adjusting end-stops incrementally.

First:

G28
G1 Z10


Then

G28
G1 Z3


Then

G28
G1 Z1


etc etc

You can also move it around in the X and Y plane:

G28
G1 Z5 X50 Y30