1st i would like to say thanks to one my reader who reported this issue, that he is unable to flash/format his corny CN-7025 tablet. he tried several methods he seen on internet but none of them worked.
i did some search and found solution for this tablet which i will write down here.

Update: easiest way i found to reset any android phone is through google itself.

to use this method, you must remember which gmail id was used in that phone & off course also password for that account.
then

1. Phone/tablet must be connect to internet (WiFi/Data)
2. visit Googel Device Manager 
3. login use same account that was used in that phone
4. and click on erase button, as shown in snapshot below
5. phone/tablet will be formatted as soon it come online.

2nd Method

1st of all you need to download the Flash file for your tab,
which you can download from this link:

and select it.

it is very important to follow all steps as described.

1. Make sure TAB is fully charged

2. Switch off TAB completely

3. Press Volume up button, and keep it pressed while you connect TAB with computer using USB cable.

4. start pressing power button repeatedly, 10-15 times while still pressing volume up button.

if you see following icon on screen, that mean you entered into download mode.

if you don’t see this logo on your screen, then you need to repeat the steps from 2-4.

and if you successfully entered in download mode.

a popup window will appear on your screen.

Important: please don’t touch any button or cable during format, otherwise you may damage your TAB.

Once finished you will see following message.

You TAB should restart and ready to use

.