Garmin has official steps for your model. Pasted below along with Garmin official link:
Step 1 -
Turn on the GPS. Enter the PIN code if you remember. If not, raise the GPS antenna so that the device can acquire a satellite signal and drive to the safety location you have programmed when first setting up the device. Driving to the security location will unlock the GPS in you do not remember your PIN.
Step 2 -
Tap the "Settings" icon on the touch screen, then select the "System" menu.
Step 3 -
Press the restore button, which is located at or near the bottom of the "System" menu. Confirm your selection by pressing "OK" when asked.
Step 4 -
Push the optional touch screen for "Garmin Lock" once the system has rebooted. Confirm your selection by pressing "DEACCORD."
Step 5 -
Enter your new PIN. You will have to enter twice, so that the second is the first . After entering and confirming your PIN a second time, touch "YES" to confirm that you want to make your new PIN.
Step 6 -
Reset the security location when prompted by touching "ACCESS." Drive to the security location of your choice and lock it in memory by pressing the "Set" button. Your PIN has been reset. Hopefully your Garmin NUVI
pin will be re set as of now.
If you do not have any idea where the safely location is then I would say you should instead follow the instructions to wipe the device to factory settings, as follows:
Note: A master reset will erase all favorites1 and will restore your device to the default factory settings. If you would like to back up your favorites to your computer, you can find instructions to do so here.
To perform a master reset on a nuvi 200, 205, 405, 500, 600, 700, 705, 1100, 1200, 1300, 1400 series, 1690, 1695, 2300 LIVE series, zumo 220, 450, 550, 660, and 665:
- Start with the device OFF and unplugged from power
- Touch and hold the lower right corner of the screen with an index finger or the eraser end of a pencil
- Continue touching and holding the lower right hand corner of the screen then power the device ON
- Release the power button when the device powers ON
- You will see a new message: "Do you really want to erase all user data?"
- Remove your finger from the touch screen when this message displays
- Touch Yes
- If text language is not in English, this is the button on the right
The device will now reset. Follow the on-screen prompts and then place your device in an area with a clear view of the sky until it acquires satellites.
1Although the master reset will erase all saved favorites, any loaded custom points of interest will remain intact on the device.