You need a Jailbroken device
Jailbreak your iPhone, iPad or iPod touch more info here.
- Open Cydia
- Tap on Sources
- Tap on Edit / Tap on Add
- Write: https://repo.xarold.com/
- Tap on Add sources / Tap on Add anyway
- Tap on Done.
Now you can install Amber from Cydia
- Tap on Search tab
- Type Amber
- Open a result, be sure you're on Xarold Repository and not another repository.
- Well now tap on Install.