want to download an app into ext sd

[Altairus]

OK so I have a fake galaxy s6 (can't afford original) but it works well and I almost can't tell the difference except for one glaring fault. The phone has two storages internal and a faux external(which is not external its just named that) each 1gb hilariously desguised as 32 each meaning when I go into the storage settings it shows each as 32gb but it gets full when I download 1 GB. I managed to pry the back case off which shouldn't be possible in an original and discovered an SD card slot which I inserted a 32 GB card in and used link2sd to store my apps. The issue righ now is that I need to download a 1.4 GB app which won't fit in 1 memory but will in my external SD. Using the storage setting doesn't work since selecting external SD card chooses the faux external card not the real one and under files the ffake external iscalled sdcard0 while the real one is called sdcard1.
So I need a way to either merge to two memories together or destroy one of them or download directly to the SD card or a custom rom do somthing like that
The model is SM-G920f
Rooted

 

[webworkings]

You should post this in the "Rooting, Jailbreaking & Unlocking" Forum. http/www.tomsguide.com/forum/forum-117.html As they can better help with setting it up on a rooted phone.