Return from external link, not showing nav-back-button



in my app, showing week diet table from external page

access to week diets table, main > buildinginfo > show diet table.

in external page, provide a fixed button to go previous page. (Why is that the Cancel button does not work.)
<div id="floatBtn" onclick="history.go(-1);"><i class="fa fa fa-chevron-left fa-3x"></i></div>

when return to app(buildinginfo page), nav-back-button gone screen, so can’t go main page.

what can i do go back main page?