How can I do factory reset on Samsung Galaxy 10.1 Tab?
If you were able to unlock the device, you would go to Settings ~> Privacy ~> Factory Data Reset &amp; follow instructions. Done!

Since you don't have access to OS, press and hold "Volume Down + Power" for 10 seconds. Screen will appear with standard Droid recovery icon. Select it with volume down key &amp; press volume up to enter. Now, you're in recovery mode from where you can factory reset your device.

Depending on your device sub-model, if its not working, try "Volume up + Home + Power" for 10 seconds. When something is displayed on screen,  release power button while holding other ones.

If this one is also not working, turn on device with power button and just after first display, press and hold "Volume up + Volume down" for 10 seconds.