But you not always will have an assistant next to you - during the liturgy and even during recitals, you have to handle the situation yourself when there is no one to turn the pages for you. Registration can be simplified but often it's the organist who has to turn the pages.
It's quite convenient to turn the pages by yourself when music layout on the page is wisely thought through by the editor. In such cases, one hand is silent for about one measure during the turn of the page. This is quite sufficient.
But don't think that even when you can do it yourself it is easy - you have to repeat this motion of the hand 10-50 times in slow motion so that your playing would not be affected by the turn. Don't take this for granted - always rehearse your page turns repeatedly.
It's even more difficult when the layout of the music on the page is rather wide and at the end of the page (when you have to do the turn) both hands are busy playing. Here's what I recommend in this case - continue your playing with the right hand and with your left make a rest and turn the page. Because the top voices sound more clear than the bottom voices, a short silence in the left hand part while you're playing smoothly will not be a problem to anyone.
PS. The technology of today has already solved this problem - when you play from your tablet, you can use a special app with the foot pedal. Simply press the pedal and the page turns by itself. But again - don't forget to rehearse this foot movement repeatedly.