Dear Gangadhar,
I will suggest to check the examples that came in the following example to check how to use the WDOG, you can found them under Code Snippets:
Arm® Cortex®-M4|Kinetis K60 100 MHz 32-bit Microcontrollers|NXP | NXP
Also this thread has an example driver that could be useful to set the module.
K60 Watchdog Refresh Issue
Regarding the implementation, you could put the refresh function in a timer interruption (LPTMR for example).
Let me know if this helps you.
Best Regards,
Alexis Andalon