GE 21SVDRWW, just bought it second hand and the "door open" alarm keeps coming on after plugging it back in. How can I fix this?

Pull the mains plug for 10 minutes. Don't open the doors, plug it back in. That should reset it.

If you have high voltage alarm, that will not stop light from coming on. Would make sure alarm is correct. First unplug fridge for 30 seconds then plug back in this should reset alarm If alarm stays off you should be OK if alarm comes back on have someone to check with voltmeter to make sure voltage is high. If not you probably need control board.

It looked like your model does NOT have an external ice/water control panel which has caused beeping problems on some models.
For your model I would try the following....
Door Alarm
The main cause of a beeping GE unit is an open refrigerator door. Some models are equipped with an internal door alarm, which trips when the door remains open for 3 minutes or longer.
One way to check this .... put your smartphone in the refrigerator on video mode and close the door. The light should go off with the door shut. If the video shows that the light stayed on when the door was closed ... then it reinforces that something is wrong with the switch/alarm. Repeat video for the freezer.
Door Seal
If beeping persists after the freezer or refrigerator door is closed, the door seals may be blocked or so dirty that the internal door alarm is tripped. The seals can be cleaned with a soft cloth and warm, soapy water. Also, an item inside the refrigerator may be preventing the door from fully closing.
Cooling System
Reactivating the refrigerator's cooling system includes a beeping noise. When the refrigerator is off, the "Off/Off" light appears on the door display. When the "Adjust Freezer" and "Energy Saver" buttons are held down for approximately 3 seconds at the same time the beep sounds and the "Off/Off" indicator disappears. Hold the "Ice Off" and "Freezer" buttons to activate the cooling system inside of the fresh food compartment. A beep signals the system is activated. The beeping should stop after the cooling system turns on. If it fails to stop, try unplugging the power cord to reset the connection.
Power
The GE's internal door alarm can get stuck. Try unplugging the refrigerator for about 10 seconds and then plug it back in. If the beeping continues, the internal door alarm might be broken or defective. Contact the manufacturer or a technician for further assistance. One way to check this .... put your smartphone in the refrigerator on video and close the door. The light should go off with the door shut. If the video shows that the light stayed on when the door was closed ... then it reinforces that something is wrong with the switch/alarm.

Good luck on your troubleshooting!

Can you post the model number? Thanks, Sea Breeze

Open freezer door. On top You will see 2 or 3 switches. Push all of them, if light in the freezer did not go off - you have bad door switch, if it did go off try same thing with fresh food door. Door switches do go bad once in a while on this fridges. Thanks

Attached is link to users manual.
Manual says that Door Alarm will sound if any door is open for more that 2 seconds and will ssop when door is closed.
Can you locate the door switches?

http://products.geappliances.com/MarketingObjectRetrieval/Dispatcher?RequestType=PDF&Name=49-60530-2.pdf

Check all your door switches by hand & see if one acts intermittently.

The default for option 10 is 30 seconds and option 11 is 60 seconds.
It sounds like option 10 is turned off because when turned off the entry delay is set to 005 seconds. All entries must be 3 digits.
You ca set option 10 and 11 from 005-254 seconds. Hope this helps