Go to samsung.com and click on Galaxy Tab, then downloads and specify your type of carrier.... then you can download the manual... a great thing!
Here's what the one for t-mobile says to reset:
Factory Data Reset
From this menu you can reset your tablet and sound settings to
the factory default settings.
1. From Idle mode, touch ➔ Settings ➔ Privacy.
2. Touch Factory data reset.
This action erases all data from your tablet except current
system software and bundled applications, or SD card files
such as music or photos.
3. Touch Reset tablet.