If you want to repair an iPhone problem with a factory reset you can use iTunes with a PC.
Step 1: Prepare your iPhone for restoration
First, launch iTunes as you would normally. Then, click the iTunes menu located on the left side of the main toolbar, select Check for Updates from the resulting drop-down menu, and ensure you have the latest version of iTunes. If not, download and install the latest version thereof. Afterward, connect your iPhone to your computer via USB and click the gray Back Up Now button when viewing the Summary tab for your given device. Alternatively, follow our guide on how to use iCloud to back up the device to Apple’s remote servers. Although backing up your device is not necessary, doing so will store your photos, apps, contacts, settings, and other data so you can automatically restore other iOS devices from the backup down the line.
If you’re using an iPhone 4S or a newer device, you might also want to disable Find My iPhone. To do so, tap the main Settings icon when viewing the home screen, select iCloud, and tap Find My iPhone. Then, toggle the slider at the top to disable the feature if you haven’t done so already.
Step 2: Restore your iPhone
Once the backup is complete, click the gray Restore iPhone button when viewing the Summary tab for your given device. Click the Restore button in the resulting pop-up window to confirm your decision, and if prompted, click Agree to agree to the software license agreement and begin downloading the necessary iOS software file before restoring.
Step 3: Ensure the phone was restored
Once the restoration process is complete — a process that may take up to several minutes — check to ensure your phone has been restored to its original factory settings. If done correctly, you’ll once again be presented with the iOS Setup Assistant upon startup, from which you can then restore your phone from a backup or continue the process as if you were setting it up anew. It’s like it just came off the assembly line in China all over again.
If you want to perform a factory reset directly on your iPhone, follow the directions on the next page.