User defined target enable when click

Hello, I am working on project use Vuforia. I use both target image and user define. I want when click on button A, start scan frame and build new target. I saw options in target builder, but actually don't need auto scan frame, because maybe user don't click button A. So how to handle or what options I need tick. Beside, maybe create user target like kudan, without camera allways parallel target to capture. Thank you so much, :).