You should be able to use the official SmartLighting feature to manage your motion sensor, then. 
See steps one through four in the following FAQ for the instructions on how to get to smart lighting.
FAQ: create a virtual three-way using the “mirror“ feature of SmartLighting [NEEDS UPDATING]
Once you are there, The device you want to control is your smart switch.
The trigger will be your motion sensor, and you will see an option there to turn the light off again after the motion stops. 