Zoom/ Focus of web app on mobile devices

I have a web app that is used on mobile phones. One of the pages has a form where the user enters information. When users tabs on one of the fields the keyboard pops up and the focus is set to that field. (the screen is zoomed in a bit)  When the user is ready entering information and leaves the field the screen is not automatically zoomed out. The result is that some buttons / information is not visible anymore.  Is it possible to actively do a rescale of the whole page         
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