(Step 1) Use miracle box
How to remove Karbonn a6+ Screen Lock with miracle box
(Step 2) Hard reset method
1: Press Power button, until your phone is off.
2: Next hold and press Volume Up + Volume Down + Power button until you see menu with 2 options.
3: From this menu choose option Recovery Mode.
Press Volume Up to enter this mode.
4: If you see Android logo on your screen, then press Power button.
5: Navigate to option "wipe data/factory reset" using Volume buttons to scroll, and Menu key + Back key to confirm.
6:Then accept this: "Yes -- delete all user data" with holding for few seconds Menu key + Back key.
7: After that confirm option "reboot".
8: That's all.
Hard Reset will erase all of your data
All described operations you are doing at your own risk.