http://www.wikihow.com/Reset-Your-Navigation-System-in-Ls430
I wrote the steps there....and here is a paste!
== Steps ==
# 1) switch of your car (I have 2005 Ls4300). The same steps could be followed on cars that have the same navigation system.
# 2) opens the trunk.
# 3) Take out the cover, as if you are looking for your spare tire. You will find a metallic box on the right.
# 4) Remove the two screws that stabilize the box with the body of your car.
# 5) plug out all the connected wires to the box. You won't need to memorize the places of the wires, since every wire has a unique shape and size that fit into its specific place.
# 6) now, take the box to a lightened place where you can see things clearly.
# 7) from the back, you will find 8 screws. Open them all
# 8) gently, remove the cover. You will find two electronic boards.
# 9) so gently, take the left one, and switches it over, where you can see its bottom side.
# 10) you will find a ribbon cable that connects the left section and the right section of the whole electronic board. Carefully, with your fingers, take off the brown small tool that stabilizes the ribbon cable with the board. This way, the ribbon will be pulled out... leave it for few seconds and then replace it to its old place.
# 11) Replace everything again to its old condition, and take the whole box and replace it in your car.
# 12) turn your car on. WAIT FOR THE SYSTEM to load. You will find a new screen with bright green colours asking for not powering off!
# 13) Nothing more, you have just maintained your navigation system.
#
# With Great thanks to PriusChat, and especially to the member "htmlspinnr"
#
