I am going to assume this is the Android one, and am including the instructions below for that. If, however, it isn't the Android one, then we would not be able to help in this thread.
How to turn off the double tap zoom (Magnification Gestures)
The double tap zoom, or Magnification Gestures as it is actually called, enables you to temporarily magnify what’s on your tablets screen.
To enable, or disable, magnification gestures you need to...
1. Go to "Settings" and then "Accessibility".
2. Next tap "Magnification Gestures".
3. Set it to either on or off, depending on which you are trying to do.
Note: When "Magnification Gestures" are turned on, you can magnify, pan, and zoom in many ways.
1. You can zoom in or out by...