I need to change time zone on atomic clock to EST

1 Insert batteries into your atomic clock. Without these the clock won't work. The number of batteries required depends on the clock. There is usually a panel on the back of the clock where you can insert the batteries.

2 Set the clock. Usually, this is done automatically, as the clock will seek out and receive the signal within 6 to 8 minutes. If this doesn't happen, you'll need to do it yourself. Hold down the "Set" button. A figure on the clock will start blinking. Adjust this by pressing the adjustment button. Press "Set" again to go to a new time. Continue until the clock is properly set. No matter what you put time you put in manually, the clock should adjust to the atomic setting within 48 hours.

3 Set the time zone on your atomic clock. How to do this depends on your specific clock. On some, there is a time zone slider; you simply slide it to your time zone. Otherwise, you will need to enter the manual mode you used to set the clock. Switch the mode until the time zone starts blinking. Now, adjust until your current time zone is selected. If it goes by Greenwich Mean Time (GMT), the time zones in the United States are -5 for Eastern time, -6 for Central, -7 for Mountain, and -8 for Pacific.

Read more : http://www.ehow.com/how_6403731_instructions-time-zone-atomic-clock.html

Radio controlled atomic clock self sets, and self adjusts automatically. This clock is very easy to use!,Daylights Saving Time on/off option; 4 Time Zones - Pacific, Mountain, Central, or Eastern,Folds into smaller size for easy storage and travel; travel pouch included,Automatically sets day, date and time; 2 separate alarms - great for weekends,Sturdy, contemporary construction. Stand folds for easy storage. 2x AAA batteries included; as shipped to U.S. Government and institutions

Instructions to set the C17D2090 atomic clock

A. To manually set the clock

1. Use the CAL/ALM button to toggle the display until it shows the calendar
2. Press and hold SET until the screen flashes "12hr"
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

This mode will let you set the 12/24 hours clock, the time, date and year. You should be in the right time zone before you start.

B. To set the alarm1 time

1. Use the CAL/ALM button to toggle the display until it shows the AL1 alarm time
2. Press and hold SET until the alarm time flashes
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

C. To set the alarm2 time

1. Use the CAL/ALM button to toggle the display until it shows the AL2 alarm time
2. Press and hold SET until the alarm time flashes
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

D. To turn on alarm1

1. Use the CAL/ALM button to toggle the display until it shows the AL1 alarm time
2. Use the DOWN (alarm) button to toggle the alarm on and off (a bell appears on the screen)

E. To turn on alarm2

1. Use the CAL/ALM button to toggle the display until it shows the AL2 alarm time
2. Use the DOWN (alarm) button to toggle the alarm on and off (a bell appears on the screen)

F. To have the atomic clock set automatically

1. Press and hold the UP (antenna) button until a little triangle flashes on the screen
2. Wait for clock to set
3. To give up waiting, press the UP (antenna) button again.

G. To change the time zone
1. Tap the ZONE button to toggle between the 4 time zones

I don't know about your atomic sync problem. But here is how you can set the time zone:

Push the Time button once. This will change the Month/Day window to Alarm 1. Push the up button until the desired time zone is reached. Push the Time button twice more to return back to Month/Day display.

Press and hold the set key until time zone appears, then + or - to your zone.

The clock will set itself at specific time set times, this is likely to be at 0200 0400 and 0600.

You will however be required to set the time zone, the switch is likely to be on the back.

INFO:
Atomic Time Synchronisation:
How does it work.
SHORT VERSION:
Radio set clocks and watches receive a 60-kilohertz, radio signal from the NIST the official timekeeper for the US and is located in Boulder, Colorado. Ft. Collins. they use atomic clocks and transmits this official time via high frequency short-wave and low frequency AM radio signals, satellite transmission, Internet, and via telephone.
　
REFERANCE LINKS:
OFFICAL TIME:
http://www.time.gov/timezone.cgi?Eastern/d/-5/java
PHOTO OF ANTANA TRANSMITTERS:
http://tf.nist.gov/stations/wwvb.htm

You didn't tell us the model number but whatever it is, you should find instructions here:
Skyscan website
Our various 'atomic' clocks have either a menu that lets one select or a simple slide switch with US time zones from which to choose. 

Online manual is at link http://skyscan.info/content/manuals/25-model-87315.html

Press and hold the "Mode" button for a few seconds until the display flashes. The briefly press the Mode button to cycle through each setting. When you get to the "Zone" setting, press the up button to advance the time zone. Press the mode button repeatedly to finish cycling through the settings.

Done.

try looking up the manual on the model number you might find it online. I have the maual for this model.