If my understanding is correct, you want this?
[quote:3ge7tox3]
(From https://www.scirra.com/manual/66/projects)
Orientations
Whether to lock the orientation on mobile devices. Any allows the display to switch between portrait and landscape automatically; choosing either portrait or landscape will attempt to lock the orientation to prevent it changing. Not all browsers or platforms support orientation locking, and in some browsers it must be in fullscreen mode (using the Browser object's Request fullscreen action) before orientation lock takes effect.
This can be set under project properties.