In the “Invite your friends to like page” window, your friends list will appear on the left side. You can select specific friends to invite, or click “select all” on the top right.
At the bottom of the window, you will also see an option to send each invite in Facebook messenger. This means your friends will receive an invite in their Facebook messenger rather than Facebook notifications.
Once you have selected your friends you would like to invite, click “Send invites” on the bottom right.