Move the Z axis up by hand turning the pulley until you get the Z axis switch to trip.
Get a piece of wood or other material that is the same thickness (or just a little smaller) as the gap between the moving Z axis carriage and the Z axis motor mounting plate. We will use this material to stop the machine without breaking your switch if homing doesn’t work right.
Move the Z axis off the homing switch by hand.
Make sure you remembered to change $1 to 255 and $21 to 0
Holding the block in place to protect your switch, in PicSender, press the $H button and get ready for the E-stop if the homing sequence doesn’t work.