I found this from Maxis Portal

Question:
I don't want my friend to check my location anymore.

Answer:
I gave a permission to check my location to a number by mistake or maybe I no longer want him/her to check my location.

In this case send "DELOK < friend's mobile number>" to 32001. You can confirm the result by sending "LISTOK" to 32001. This will give you a list of phone numbers that can track your location.