15. how to install/eject the micro SD card?

A: The X5III/X7MKII can support two micro SD cards with the capacity up to 256GB.  And the card of class 10 (or above level) is recommended.

There are two concealed micro SD card slots at the right side of the X5 3rd gen/X7MKII. To install the cards, you can first use the supplied card tray ejector pin to poke the little hole on the card tray, then it will pop up.  After that pull out the card tray, install the micro SD card onto the tray holder (in the direction showed in the below images), and then insert the card tray with cards back into the slot.

The right way to put the microSD card and card tray together is as follows: