Turn off your Hyundai Elantra.
Use a Phillips screwdriver to remove the four screws holding the dash shroud, which is the plastic in the middle of the dashboard, in place.
Locate the ETACS module behind the ashtray. The ETACS is the computer the controls the alarm, turn signals and keyless entry. It should be visible as soon as you remove the dash shroud.
Locate the tiny DIP switches on the ETACS module. There should be two remotes, one labeled "1" and the other labeled "2."
Flip the switch labeled "1" on the ETACS module. On the keyless remote, there is a button labeled "1." Press the "1" button on the remote, and then flip the "1" switch on the ETACS module back to its original position. Repeat this process with the "2" switch on the ETACS module and the "2" button on the keyless remote.
Reattach the dash shroud with the four screws and the Phillips screwdriver.