I'll do my best to help you. Im no expert. Could others please help if I'm wrong.I have a iPad and a iPhone SE
Both don’t show the option
I fly with my iPad mini 4 when I'm overseas with no cell ( No sim) installed.
I have not been os with my Crystalsky yet.
I'm hoping your iPad is a cellur one and only couple of years old.
Older apple products don't preform well with the latest Mavic firmware.
I'm not sure your iPhone SE will be able able to cut it.
2 ways to do it.
When you are out in the field with no cell the built in GPS in your Apple devise loads the maps.
Just start the Mavic & controller. Hook up the Apple. Start GO4 and the maps with slowly load via GPS. this may take a few minutes.
Option 2.
Before you go to your location and you and you have wifi
Do the same as above ( You don't have to start the drone)
In the go4 app ( Camera View) open the maps and pinch out on the maps screen to find the locations you wish to fly. This will load the maps in the cache in the device you are using.
This will store it for you. When you go to fly the maps will be there.
Get on Youtube search for setting up your Mavic. There will be heaps of info.
Cheers
Marty