Keychain items are in iOS sandbox, users don’t have access to remove unwanted keychain item. These are accessible via API’s only.
KeychainItemWrapper *keychainItem = [[KeychainItemWrapper alloc] initWithIdentifier:[[NSBundle mainBundle] bundleIdentifier] accessGroup:nil];
//or how you access your keychain
[keychainItem resetKeychainItem];
or you can reset your device >> from the device Settings, General, Reset, Reset All Settings.
But, it will reset the keychain for every app installed on the device.