There are two ways for you to restore the iPhone. You can have a try.
1. Using iTunes. Connect your iPhone with the computer. Then open iTunes > iPhone icon > Summary > Restore. After that, your iPhone will be restored, but this may lead to data loss sometimes.
2. Using a third-party tool. Any iOS system repair programs such as TunesKit iOS System Recovery can restore your iPhone without data loss. And there are only three steps you need to follow.
When you get a new phone, it is tempting to want to play with it. You may want to see what functions and buttons do. Sometimes, this can cause problems. The user may have trouble getting the phone to function the way it did before. However, there are steps you can do in order to get the phone back to the way it was.
One way to do this is by connect the phone to your laptop. You will want to save the data that you already have so that it will not erase things that you need on your phone. In itunes, you can click restore a few times and then you will need to wait. Once the itunes is finished, it should restore your phone back to the way it once was.