STEP 1: While logged in on your personal profile, Facebook and click on “Build Audience” on the top right side of the Facebook page you admin and the click “Invite Friends” button.
NOTE: you need to be logged in as your personal profile while accessing the page. If you don’t see the option to “Invite Friends”, from your personal FB acount type your page’s URL directly into the browser URL bar and go straight to it. That should make it possible to get to step 2.
STEP 2: Scroll down till it loads every single friend you have on your list. you have to keep scrolling down until it stops loading more.
NOTE: If you want to only invite specific people, you can chose from the filters that are available here before scrolling.