Running the MYTASK from the PX4 Documents

Hi there, So i am learning the PX4 environment from last two weeks. I need help to find/solve/run the MYTASK in flight Task page. I exactly did as what the doc explained. Testing the flight task is the one i am hanging around, i don’t understand the concept of testing the flight task.
" To test the flight task you need to run the vehicle with the task enabled. For the example above, this means setting the parameter MPC_POS_MODE to 5, taking off, and switching the vehicle to Position mode."

As it says to enable the task we have to set the parameter 5 in MPC_POS_MODE. I don’t know where do i have to set it. i tried so many times. But it didn’t get right.

Thanks in advance