The process is going to depend on which model of phone you have. Most Android phones you can swipe from the top of the screen down and inside your quick settings toggles you should see an icon for a flashlight for which you would tap on and or off. After doing so most phones on the lockscreen will have an indication that the flashlight is still on and you can tap the notification to turn it off again. On an iPhone you would swipe up from the bottom and control center and your flashlight would be there to toggle on and off. If your phone does not have a flashlight app you can download one from the App Store like Google Play.
Hey there! Were you able to find the flash light option on your phone?