You can easily do this with the built-in tool of iOS.
Go to Settings of iOs
Drag down on the list to bring out the search bar. Type Zoom (see image below)
Turn on "Zoom"
Now, you can double tap using 3 fingers to bring out the magnifying glass.
Double tap and hold your 3 fingers, then slide up to zoom in.
To resize the magnifying glass, you can triple tap using 3 fingers.