Adding an already installed game
This is the easiest and recommended way to go. First install the game on a desktop PC and then copy it over to your mobile device. As an example we will install a hypothetical game. Let's call it
"Battle Tanks".
How to start
Following this
game copy tutorial we have the Battle Tanks files in a folder called "BTanks" with
game data inside our Drive_C folder.
/storage/emulated/0/Drive_C/BTanks

Pushing this icon on the main screen will create a new temporary game profile. It won't be added to your collection until it's confirmed.
Icon and description
On top of the dialog page you can customize your game profile. We'll pick a downloaded game box-art cover and set the game name - "Battle Tanks".
Below these settings are two additional sections
•Hardware
•Software
Hardware
The name says everything. In this section we define computer components. Fortunately the default settings for Magic DOSBox are pretty good, and we won't need to modify additional settings
except for desired memory size and the Drive C:\ location. For Battle Tanks we are setting 8MB for memory.
Scroll to "Drive C:\" options and hit the "Choose" button. Navigate to the Drive_C folder and pick it.
NOTE : if you've gone inside the BTanks folder, back up -- you've gone too deep!
HINT : the path to Drive_C can be configured in "Global Settings". This will be the default for every new profile.
Software
In this section we tell Magic Dosbox which game should run. Old games have usually two starting programs. One that starts the game and the second which loads the
game configuration program - usually called "setup".
Tap the "Choose" button for "Main program" and navigate to the BTanks folder which should be inside the Drive_C folder. In the BTanks folder select BATTLE.EXE. That's all we need for now.
Confirm the game profile changes. This will add Battle Tanks to our collection. If you want to start the game just tap on the game profile image. Use a long-press on the profile image for
additional updates.