If this is new record in the Records menu, you'd need to set up the layout with a custom menu that performs a script when New Record is selected.
You can then put your popover on your layout and use the Inspector to give the Popover Panel (NOT the button) an object name such as "New Record Popover".
Then your script can use:
Go to Object ["New Record Popover"]
to open the popover.
Note that this same method can be used in a script to select a specific tab or slide control panel.