UI actions are triggered when they're clicked, you can't call them from somewhere else.
What you could do is write the code you need in a script include and then call that from the UI action and from your scheduled job. Or just copy the code from your UI action into your scheduled job and make the changes that'll be needed to make it work.
It depends what your UI action is doing but as long as your UI action is only running server side code it should be fine.
