How to home only ONE axis in Marlin

In the Marlin 3D printer firmware, you can home one axis without homing the other axes using G28[Axis].

In order to home the X axis:

G28X

In order to home the Y axis:

G28Y

In order to home the Z axis:

G28Z

You can also home multiple axes using G28[Axis 1][Axis 2]. So in order to home the X and the Y axis (but not home the Z axis), run

G28XY