We purchased a 03 lincoln lsand need to reset the keyless entry

1. Sit in the vehicle driver's seat.
2. Remove the ignition key from the ignition lock cylinder.
3. Close all of the vehicle's doors.
4. Remove the MALL PGM fuse from the fuse panel. Or reset the fuse which controls your keyless remote.
5. Turn the ignition lock cylinder to the ACC position.
6. Turn the ignition lock cylinder OFF, then back to ACC within 1 second.
7. Open and then close any vehicle door. You will hear a chime when the
remote control door lock receiver enters the programming/diagnostic mode. If
you do not hear a chime, start again at step 1.

This is an important fact here:

After 7 seconds, you may hear a chime confirming successful synchronization.
After approximately 14 seconds, you will hear a chime confirming successful
programming.

8. Press and hold the transmitter LOCK and UNLOCK buttons simultaneously for
14 seconds.
9. Repeat step 8 in order to program each additional transmitter.
10. Remove the ignition key from the ignition lock cylinder.
11. Install the MALL PGM fuse back into the fuse panel.

This is important as well:
Once the keyless entry receiver enters the programming/diagnostic mode, the
programming of the first transmitter erases all previous transmitter
programming information. You must then program all of the transmitters.
Program only 1 vehicle remote control door lock receiver at a time. If you
program multiple receivers simultaneously, the same transmitter could
possibly be programmed to more than 1 remote control door lock receiver

The fuse should be in your fuse block of your vehicle.