PCA9685 plugin gives only the raw value and to control the servo you will need to edit the plugin code or add a new servo plugin based on PCA9685 (this is bit difficult)
A simple approach is to combine Using the Adafruit Library | Adafruit 16 Channel Servo Driver with Raspberry Pi | Adafruit Learning System with GitHub - myDevicesIoT/Cayenne-MQTT-Python: Python Library for Cayenne MQTT API