First, you have to have an app store account. If not, please register one first, so I won't go into details here.

Then, go to the appstore and click the search below.

Enter the search location: "qq20 13HD".

At this time, a bunch of things related to this keyword may come out. You need to eliminate them and find the real QQ20 13.

Then click Install and enter your appstore account password, and the installation will be completed automatically.