Here's the instructions from the manual:
1. Press and hold the two outside
buttons releasing only when the
indicator light begins to flash after
20 seconds. Do not repeat Step 1
to program additional hand-held
transmitters to the remaining two
HomeLink buttons. This will erase
previously programmed hand-held
transmitter signals into HomeLink.
2. Position the end of your
hand-held transmitter 1–3 inches (2–8 cm) away from the HomeLink
button you wish to program (located on your visor) while keeping the
indicator light in view.
3. Simultaneously press and hold
both the HomeLink and hand-held
transmitter button. Do not release
the buttons until Step 4 has
been completed.
4. The indicator light will flash slowly and then rapidly. Release both
buttons when the indicator light flashes rapidly. (The rapid flashing light
indicates acceptance of the hand-held transmitters’ radio frequency
signals.)
5. Press and hold the just-trained HomeLink button and observe the
indicator light. If the light is constant, programming is complete and your
device should activate when the HomeLink button is pressed and
released. Note: To program the remaining two HomeLink buttons,
begin with Step 2 in the “Programming” section — do not repeat Step 1.
Note: If the indicator light blinks rapidly for two seconds and then turns
to a continuous red, proceed with Steps 6 through 8 to complete
programming of a rolling code equipped device.
6. At the garage door opener receiver (motor-head unit) in the garage,
locate the “learn” or “smart” button (usually near where the hanging
antenna wire is attached to the unit).
7. Press and release the “learn” or “smart” button. (The name and color
of the button may vary by manufacturer.)
Note: There are 30 seconds in which to initiate Step 8.
8. Return to the vehicle and firmly press, hold for two seconds and
release the HomeLink button. Repeat the press/hold/release sequence
again, and, depending on the brand of the garage door opener (or other
rolling code equipped device), repeat this sequence a third time to
complete the programming.