The Push should automatically work with Melodics once it has been run (at least once) with Ableton Live.
But Ableton Live will take priority. Melodics will only correctly connect when Ableton Live is not open.
Melodics connects to the Live port of the Push, if the hardware does not connect in Melodics it may be in User mode. To change to Live mode:
Open Ableton Live (this should automatically connect to your Push 2, provided you have gone through the Push 2 setup)
If in user mode the User button should be lit, press this to switch out of User mode
And you should be ready to go!