Activate Fingerprint Scanner from Off(default)

Hi, I am using fingerprint scanner as the authentication method in my project.

But I am facing some problems...

Do anyone know how to turn on the fingerprint scanner only after "ON" button is pressed in the android apps. I am using HC-05 bluetooth module to connect both Arduino and android studio together. So what I want to ask is how to activate the fingerprint scanner only after button pressed? What is the code do i need to add on in my Arduino Coding?

Can you show your arduino code?