It may be difficult to position the page number and the running head on the first page and then format them differently on subsequent pages.
Watch all or part of this 18-minute YouTube video which explains how to set the format in Word using Windows. Here are the time segments in case you want to skip around the tutorial:
Source: Samuel Forlenza, published January 6, 2018 on YouTube.com
Tutorial by Terrance D. Jorgensen, Kennesaw State University, Kennesaw, GA demonstrating how to type a paper using APA format on a Mac computer.
This is a 10-min. video.
Note: The new 7th edition of the Publication Manual of the American Psychological Association has arrived in October 2019. Watch for details.