On the LCS App, when you're in the "Edit" screen, select the push button and then select the gear symbol to enter the settings for the push button. The default is for the ASC2. Did you swipe right to select the ACS? The screen will then look like this:
Press the gear again, make sure the correct TMCC ID is entered in for the accessory, and then select "Save"
Let me know if this works.