Hi - These are the directions for the 1999 ES300. I would guess it works the same as the RX.
Here are the directions right out of the owner's manual. For easy online access to the owner's manual, you should register your car at lexus.com - it's quick, easy, and very informative. Here's the link:https://auth.owners......2fssl/Welcome
The HomeLink has 3 buttons and can be
programmed to operate 3 separate devices.
Prepare the HomeLink for programming by
erasing all codes or the memorized data
programmed by the former owner.
Erasing the garage door opener memory
Push and hold down the 2 outside buttons for about 20
seconds until the indicator light flashes. All memorized
data will be erased.
1. Decide which one of the 3 buttons you want to
program. Push and hold down the button for about 20
seconds until the indicator light begins to flash. While
holding this button, follow steps ”2” and ”3”.
2. Bring the hand held garage door opener within about
25 mm (1 in.) of the button being programmed and push
the button on the hand held garage door opener. The
signal from the hand held garage door opener is sent to
the vehicle’s opener.
3. When the frequency and code is registered, the
indicator light flashes rapidly. At this point, you can
release both buttons.
4. To program the remaining buttons, repeat steps ”1”
If you want to replace an existing program with a new
program, select the button you want to program. Follow
the procedure from step 1.
If the transmitter has a ”rolling code feature”, it is
necessary to program the in–garage receiver after
1. Locate the ”training” or ”learning” button on the
in–garage receiver and push and release this
button. Location of the button may vary by the
garage door opener manufacturer.
2. Firmly push and release the trained HomeLink
button 2 times (some garage door manufacturer
may require you to push the HomeLink button up
to 3 times) to complete the process.
The garage door should now operate when the
HomeLink button is pushed.