Understand that flashing back using the JF6 one click will not take you back to perfect AT&T stock. JF6 one click ROM cannot be updated using the AT&T over the air. You'll need to use KIES to do the update if you want to (I wouldn't suggest it- it removes USB tethering).
If that's okay, and you still want to proceed-
First read and understand the (somewhat vague) instructions given in the first post of this thread here:
[STOCK ROM] Odin3 One-Click Downloader and Drivers CAPTIVATE ONLY - xda-developers
The one-click version I'm talking about is listed here also, under the following text (url won't work below because of the dots):
http://www.thevod.org/misc/captivate...l-OCD-REV0.rar
Make sure you have the correct drivers installed (linked in that post too).
First, back up everything you want to keep that is currently on the phone- pictures, music, ringtones etc. Move it to your PC or to the external SD card.
(Optional) If you want to start completely fresh, perform a master clear (erases everything). To do this,
0) Unplug phone from PC
1) start Odin
2) put phone into usb debug mode,
3) and plug in the phone USB cable. Odin should recognize the phone as connected (if not, check PC drivers).
4) Press "master clear". Leave the phone alone until you get "all threads completed" status message. It might reboot a couple of times.
To restore the phone to "stock" (actually, it's not perfectly stock, see first paragraph)
0) Unplug phone from PC
1) Start Odin (if necessary)
2) Boot phone into download mode (method below worked for me)
Method 3
KEY COMBO)
Remove the battery, sim card, sdcard if you have one
Insert the battery
Hold both Volume buttons
Plug in the USB cable and continue holding both Volume buttons
You should boot to a screen where you see a droid digging with a shovel.
If not, either try again (easy to slip with the keys), or try a different method from the xda post linked above.
3) Odin should have recognized the phone connection
4) Press "START"
5) Again - leave the phone alone until you get "all threads completed" status message. It might reboot a couple of times.
6) Hopefully you're up and running.
7) .... if you like, press the thanks button on the post, it makes me happy.
Hope this helps,
AoN