Is your phone is stuck in a loop whereby when you tap "Set as default" and then "Agree & Set as Default", it sends you back to the initial "Set default launcher" screen?
The quickest solution is to restart the phone.
Simply press the upper volume button on the left-hand side of the phone and the power button on the right-hand side of the phone at the same time, then click the "Restart" option that appears on the screen.
If this doesn't work, contact us right away at [email protected].