Recently, I had to restore my Prestigio tablet to its factory settings. I could not find exact instructions specific for that model that work stright forward, so I had to make guesses based on the information found on the net.
So, to make a hard reset on Prestigio 3870C_DUO, follow the steps below:
1. Power off the tablet by holding the power button for a few seconds.
2. Press the power and volume+ buttons simultaneously and hold them until the boot screen comes up.
3. Then release the power button, but keep holding volume+ for another 2-3 seconds. After releasing the volume+ button, the screen will go black for a few seconds and the android system recovery menu will appear.
4. Use volume+/- buttons to go through the menu options and select “wipe data/factory reset” using the power button.
5. Optionally, after step 4, you may wipe the cache and media partitions in the same way if you do not have important data stored there.