iPhone full screen landscape only, how to do auto orientation?

Hello, just a simple question but I haven’t yet find an good answer.

As titled, my app is landscape and I want it full screen only; and I don’t know how to make it auto-rotate…

in iOS Export option I can just check the “auto orientation”, but when I hold my iPhone upright it will rotate and shrink the app so it’s still landscape but fit in the (upright) portrait screen… I don’t want that…

Any help is appreciated.
Thanks guys and Happy New Year!!!