A picture of the Restart App on the third page of your phone
The Restart App was an app used to delete all of your data. It would not delete just your phone data, but all of your progress, including your money, furniture, blueprints, cars, codes, and more.
It was suggested that you don't use this app, but if you want to start from the beginning, this was how. Go to the third page on your phone, and click the "Restart" app. It would ask you if you are sure to make these changes. If you press "Yes", then all of your data would be deleted. If you change your mind at the last second, you could press "Cancel" to abort the process. If you do delete your data, there is no way to get it back.
Please be aware that if you are to reset, you cannot redeem the codes you have already redeemed.