I bought my macbook from someone last month.i tried doing some update and its asking me of firmware lock code

It says

"If you forgot your firmware password

If you can't remember your firmware password, schedule an in-person service appointment with an Apple Store or Apple Authorized Service Provider. Bring your Mac to the appointment, and bring your original receipt or invoice as proof of purchase."

Or you can have the person you bought it from do this:

"How to turn off a firmware password

1. Start up from macOS Recovery. During startup, you will be prompted to enter the firmware password.
2. When the utilities window appears, click Utilities in the menu bar,
3. then choose Startup Security Utility or Firmware Password Utility.
4. Click Turn Off Firmware Password.
5. Enter the firmware password again when prompted.
6. Quit the utility, then choose Apple menu  > Restart. "

Tbere would be little sense in setting a firmware password if it could be reset or bypassed by anyone but the person who set the password. It is a deterrent against stealing then selling Macs.

Set a firmware password on your Mac - Apple Support

Scroll down to the section about forgetting the firmware password.

You did not read the info at the link I posted above. You can't reset the firmware password.