You don't. LG and Samsung wisely removed that "capability" (it's more like "abortion") from their phones. For, as SpookDroid said, has many hassles, one of which, in my opinion, is turning a card that should last until 200GB of storage is a joke into a useless card in months. (I still have perfectly working 32MB cards. Who wants one card with 1/30th of a GB on it?)
If the part of the app that saves its current state gets moved to the card, it can be writing to the card a few hundred times a minute. SD card lives are measured in write cycles (which is a huge number, but nowhere near infinite), so writing to it a few million times a day can kill the card quickly. (eMMC storage, what's inside the phone, doesn't have that problem as much - the phone will be useless before the storage is.)
Also - if the card goes bad and you have apps installed on, or moved to, it, you've lost the use of the app. But you can't install it again, because, as far as the system is concerned, it's already installed. The normal solution is to just uninstall it first. But you can't do that because it's not there to uninstall. So you do a total backup on whatever is still working on the phone, then do a factory reset, then restore everything you backed up. Every time an SD card goes bad.
There are more reasons, but that should be enough to show you why putting apps on the SD card, moving or using the card as internal storage, is one.of.the.bad.ideas.of.the.century.
Buy a phone with enough internal (eMMC) storage for as long as you plan to keep it. Use SD cards to store data (pictures, documents, music, videos, etc.)